According to ReadWriteWeb, though, they are only supporting h.264 encoded video. If you use Firefox, you are out of luck. I tried to find a hack, a way on my Mac anyway to get Firefox to work with this h.264 based beta test to no avail. I find that surprising and suspect it has more to do with YouTube than Firefox.
As excited as I would be at Google’s move to support an open standard, I am skeptical since this doesn’t include video in third party sites. Technically, that makes sense. All of the embed codes to date have used the necessary markup to drive the Flash player. There isn’t any effective way to retrofit those to use HTML5 and even going forward, HTML5 just isn’t widely supported enough for it to make sense for YouTube to use it in its embed codes just yet.
On the whole, I’ll still choose to interpret this as a good step forward for open video. Maybe with Google’s recent acquisition of On2, the future of open video as part of HTML5 adoption still has some fight left in it.