"Wired, with the help of users on the VR-Zone forums, has uncovered a simple way to get high-quality uploaded videos to display in 1280x720--also known as 720p.
YouTube has long been expected to roll out high-definition video playback, and this appears to be the first viable way to do it. The hack in question is similar to the one that was first used to toggle on the "high quality" mode. It is done simply by adding "&fmt=22" to the end of the video URL...."
http://news.cnet.com/8301-17939_109-10104182-2.html