Sign up for the beta on this page, and boom, you get videos using H.264 and the HTML5 video tag instead of Flash. Working great for me. Note, though, that it only applies to videos on youtube.com itself — YouTube videos embedded in web pages on other sites still use Flash.
Update: It’s worth noting that YouTube is only supporting H.264, so it only works with Safari and Chrome, not Firefox. (Firefox supports only the Ogg Theora format. Don’t hold your breath waiting for YouTube to re-encode everything in Ogg Theora.)
★ Thursday, 21 January 2010