Aaaand, it works! But you'll only be able to see it if you've got a browser that supports HTML 5... Firefox 3.5, for example.
What's so great about this is that to post a video, all you have to do is use the <video>, like so:
But companies like Adobe and Microsoft don't really like this, because then Flash & Silverlight become redundant and too difficult for playing video files on web-pages. So... support standard compliance, use Firefox :)
Though, I must admit that the support is rather buggy at the moment. Not make it not autoplay, you have to exclude the autoplay parameter entirely from the tag. The same goes for the controls parameter. And it seems that the tag doesn't want to terminate normally without being enclosed in another tag (I used <span>)