Excellent job! I love url hacking =). I still frequently type "repeat" after "youtube" in order to loop songs, but I probably wouldn't bother to cut and paste the url into a third party site.
Along those same lines, if you feel like doing some related hackery, I'd love to see a youtube video (and audio) reverser. Sometimes people stick reversed audio in their videos, and I'd like to hear it played back the right way around; right now, I do that via youtube-dl and audacity, which is a pain. As far as I can tell, there aren't any reverse video players around at all.
hmmm....that would be really interesting. What type of use do you see for it? I think it'd be neat too :O