This is my testing setup: I created a new database (test) that doesn't use any VHost rules.

Inside it I created a design document that only has rewrites field.  There are three different rewrite configurations I used and 4 commands that I ran. For each command run I provide exact command I used, the output, my comment
of the output and relevant log from couch.log.

I always sent the same document contained in file "example" - namely:
{
    "type": "comment"
}

Below are the test results:
----------------------------------------------------------------------------------------------------
## Test 1:
# rewrites config:
[
   {
       "to": "../..",
       "from": ":db"
   }
]

---------------------

# Executed command 1.1:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/
{"ok":true,"id":"ce8b504d63666c9257cc07537c00aa70","rev":"1-505a221d0aef5d664f29d6afdae01293"}

# Comment: expected result - everything is fine.

---------------------

# Executed command 1.2:
$ curl -X PUT  -d @example -H "Content-type:application/json"  http://localhost:5984/test/_design/test/_rewrite/test/randomid324324
{"error":"not_found","reason":"missing"}

# Comment: result expected since there is no ID parameter passed through - due to the rewrite rule

#LOG:
[Mon, 10 Jan 2011 21:42:17 GMT] [debug] [<0.8844.3>] 'PUT' /test/_design/test/_rewrite/test/randomid324324 {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 21:42:17 GMT] [debug] [<0.8844.3>] OAuth Params: []

[Mon, 10 Jan 2011 21:42:17 GMT] [debug] [<0.8844.3>] Minor error in HTTP request: not_found

[Mon, 10 Jan 2011 21:42:17 GMT] [debug] [<0.8844.3>] Stacktrace: [{couch_httpd_rewrite,handle_rewrite_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 21:42:17 GMT] [info] [<0.8844.3>] 127.0.0.1 - - 'PUT' /test/_design/test/_rewrite/test/randomid324324 404

[Mon, 10 Jan 2011 21:42:17 GMT] [debug] [<0.8844.3>] httpd 404 error response:
 {"error":"not_found","reason":"missing"}

---------------------


# Executed command 1.3:
$curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/_design/test/_rewrite/test/
{"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

# Comment: Rewrite is wrong - also peculiar it won't take application/json content type.

# LOG:
[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] 'POST' /test/_design/test/_rewrite/test/ {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] OAuth Params: []

[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] rewrite to "/test/_design/..?db=test"


[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] 'POST' /test/_design/..?db=test {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] OAuth Params: [{"db","test"}]

[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] Minor error in HTTP request: {bad_ctype,

                                 "Content-Type must be multipart/form-data"}

[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] Stacktrace: [{couch_httpd,validate_ctype,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 21:51:55 GMT] [info] [<0.9453.3>] 127.0.0.1 - - 'POST' /test/_design/..?db=test 415

[Mon, 10 Jan 2011 21:51:55 GMT] [debug] [<0.9453.3>] httpd 415 error response:
 {"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

---------------------

# Executed command 1.4:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/randomid32420
{"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

# Comment: I did this one just because - and I noticed that when you post with and ID - it wont accept JSON content type

# LOG:
[Mon, 10 Jan 2011 21:54:23 GMT] [debug] [<0.9490.3>] 'POST' /test/randomid32420 {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 21:54:23 GMT] [debug] [<0.9490.3>] OAuth Params: []

[Mon, 10 Jan 2011 21:54:23 GMT] [debug] [<0.9490.3>] Minor error in HTTP request: {bad_ctype,

                                 "Content-Type must be multipart/form-data"}

[Mon, 10 Jan 2011 21:54:23 GMT] [debug] [<0.9490.3>] Stacktrace: [{couch_httpd,validate_ctype,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 21:54:23 GMT] [info] [<0.9490.3>] 127.0.0.1 - - 'POST' /test/randomid32420 415

[Mon, 10 Jan 2011 21:54:23 GMT] [debug] [<0.9490.3>] httpd 415 error response:
 {"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}



----------------------------------------------------------------------------------------------------


## Test 2:

# Rewrites config:
[
   {
       "to": "../../*",
       "from": ":db/*"
   }
]

# Executed command 2.1:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/
{"ok":true,"id":"ce8b504d63666c9257cc07537c00af99","rev":"1-505a221d0aef5d664f29d6afdae01293"}

# Comment: OK, everything is fine

---------------------

#Executed command 2.2:
$ curl -X PUT  -d @example -H "Content-type:application/json"  http://localhost:5984/test/_design/test/_rewrite/test/randomid3125
{"ok":true,"id":"randomid3125","rev":"1-505a221d0aef5d664f29d6afdae01293"}

# Comment: OK, everything is fine - since now rewrite rule appropriately handles the ID.

---------------------

#Executed command 2.3:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/_design/test/_rewrite/test/
{"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

# Comment: Routing and content type are wrong (routing in PUT request - command 2.2 was done right!)

# LOG:
[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] 'POST' /test/_design/test/_rewrite/test/ {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] OAuth Params: []

[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] rewrite to "/test/_design/..?db=test"


[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] 'POST' /test/_design/..?db=test {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] OAuth Params: [{"db","test"}]

[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] Minor error in HTTP request: {bad_ctype,

                                 "Content-Type must be multipart/form-data"}

[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] Stacktrace: [{couch_httpd,validate_ctype,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 22:06:17 GMT] [info] [<0.10262.3>] 127.0.0.1 - - 'POST' /test/_design/..?db=test 415

[Mon, 10 Jan 2011 22:06:17 GMT] [debug] [<0.10262.3>] httpd 415 error response:
 {"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

---------------------

#Executed command 2.4:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/randomid32843
{"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

#Comment: No routing information in log, got Cotent type error.

#LOG:
[Mon, 10 Jan 2011 22:11:53 GMT] [debug] [<0.10377.3>] 'POST' /test/randomid32843 {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 22:11:53 GMT] [debug] [<0.10377.3>] OAuth Params: []

[Mon, 10 Jan 2011 22:11:53 GMT] [debug] [<0.10377.3>] Minor error in HTTP request: {bad_ctype,

                                 "Content-Type must be multipart/form-data"}

[Mon, 10 Jan 2011 22:11:53 GMT] [debug] [<0.10377.3>] Stacktrace: [{couch_httpd,validate_ctype,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 22:11:53 GMT] [info] [<0.10377.3>] 127.0.0.1 - - 'POST' /test/randomid32843 415

[Mon, 10 Jan 2011 22:11:53 GMT] [debug] [<0.10377.3>] httpd 415 error response:
 {"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

----------------------------------------------------------------------------------------------------


## Test 3:

# Rewrites config:
[
   {
       "to": "../../*",
       "from": ":db/*"
   },
   {
       "to": "../..",
       "from": ":db"
   }
]

---------------------

# Executed command 3.1:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/
{"ok":true,"id":"ce8b504d63666c9257cc07537c00bbe3","rev":"1-505a221d0aef5d664f29d6afdae01293"}

# Comment: OK! works as expected

---------------------

#Executed command 3.2:
$ curl -X PUT  -d @example -H "Content-type:application/json"  http://localhost:5984/test/_design/test/_rewrite/test/randomid43242
{"ok":true,"id":"randomid43242","rev":"1-505a221d0aef5d664f29d6afdae01293"}

# Comment: OK! works as expected

---------------------

#Executed command 3.3:
$ curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/_design/test/_rewrite/test/
{"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

# Comment: Rewrite issue and content type issue

# LOG:
[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] 'POST' /test/_design/test/_rewrite/test/ {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] OAuth Params: []

[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] rewrite to "/test/_design/..?db=test"


[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] 'POST' /test/_design/..?db=test {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] OAuth Params: [{"db","test"}]

[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] Minor error in HTTP request: {bad_ctype,

                                 "Content-Type must be multipart/form-data"}

[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] Stacktrace: [{couch_httpd,validate_ctype,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 22:19:55 GMT] [info] [<0.11199.3>] 127.0.0.1 - - 'POST' /test/_design/..?db=test 415

[Mon, 10 Jan 2011 22:19:55 GMT] [debug] [<0.11199.3>] httpd 415 error response:
 {"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

---------------------

#Executed command 3.4:
$  curl  -d @example -H "Content-type:application/json" -e http://localhost:5984/test  http://localhost:5984/test/randomid432432
{"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}

#Comment: Obviously no rewrite issue, however content type problem is there

#LOG:
[Mon, 10 Jan 2011 22:21:24 GMT] [debug] [<0.11220.3>] 'POST' /test/randomid432432 {1,1}
Headers: [{'Accept',"*/*"},
          {'Content-Length',"23"},
          {'Content-Type',"application/json"},
          {'Host',"localhost:5984"},
          {'Referer',"http://localhost:5984/test"},
          {'User-Agent',"curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18"}]

[Mon, 10 Jan 2011 22:21:24 GMT] [debug] [<0.11220.3>] OAuth Params: []

[Mon, 10 Jan 2011 22:21:24 GMT] [debug] [<0.11220.3>] Minor error in HTTP request: {bad_ctype,

                                 "Content-Type must be multipart/form-data"}

[Mon, 10 Jan 2011 22:21:24 GMT] [debug] [<0.11220.3>] Stacktrace: [{couch_httpd,validate_ctype,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request_int,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}]

[Mon, 10 Jan 2011 22:21:24 GMT] [info] [<0.11220.3>] 127.0.0.1 - - 'POST' /test/randomid432432 415

[Mon, 10 Jan 2011 22:21:24 GMT] [debug] [<0.11220.3>] httpd 415 error response:
 {"error":"bad_content_type","reason":"Content-Type must be multipart/form-data"}