You know if you've asked them not to use Flash...
The only way to get h.264 or WebM videos out of Flash (which doesn't do WebM) is to go to http://www.youtube.co.uk/html5 and press the big button.
Then *some* videos will play in the new crappy non-flash method. Just try for full screen playback! Never mind smooth full screen playback...
And some of the "known issues":
Fullscreen support is partially implemented. Pressing the fullscreen button will expand the player to fill your browser. If your browser supports a fullscreen option, you can then use that to truly fill the screen.
If you want to find videos with WebM formats available, you can use the Advanced Search options to look for them (or just add &webm=1 to any search URL).
Video annotations are not supported in the HTML5 video player
Additional Restrictions (we are working on these!)
Videos with ads are not supported (they will play in the Flash player)
On Firefox and Opera, only videos with WebM transcodes will play in HTML5
If you've opted in to other testtube experiments, you may not get the HTML5 player (Feather is supported, though)