No way to disable quoting playable uris

I cannot reproduce with Vimeo videos specifically, although I can observe that quoting the example URI that you give indeed fails.

Here is what happens when I try to play e.g. the first video of the HD channel ("Phoenix - 1901 - A Take Away Show"):
 - unquoted URL: http://vimeo.com/moogaloop/play/clip:7942520/063aa13b9e53ae2fa551a8f7cdeca33b/1259933400/?q=hd
 - quoted URL: http://vimeo.com/moogaloop/play/clip:7942520/063aa13b9e53ae2fa551a8f7cdeca33b/1259933400/%3Fq%3Dhd

which is then successfully redirected to http://bitcast.vimeo.com/vimeo/v2/125/878/12587819.mp4?e=1259934410&h=c94226a1f866b49aaf12be4cf7f4a3f2

You can't reproduce with Vimeo because I have commented out the failing code, and as per our discussion yesterday it seems it wasn't even needed because my problems were caused by a faulty gstreamer install.

Nevertheless, it should be possible to inhibit the quoting or override the allowed characters, maybe.

Can be observed in the grooveshark plugin. Steps to reproduce (from bug #493571):

1. Launch Moovida
2. Go to Grooveshark plugin->Popular->Songs
3. Try to play any song

Note that in bug #502488 Guillaume proposes a patch that consists in adding "special" characters (";/?:@&=+$,") to the unescape list. It sounds like a valid solution for standard remote resources, but will most likely fail for local files, for which the original escaping has been introduced.
IMHO, the escaping should be done for local files only, before building MediaUri objects. Not in the player's code.

I think the proper way to fix this would be either to escape *before* creating the MediaUri as you suggested or to escape each parameter individually in the MediaUri object before reconstructing the URI string (that way the param delimiters won't be escaped).

The following plugin updates have been published in the plugin repository to fix the issue:
 - gstreamer 0.12.1
 - poblesec 0.21.1