Ryanne, Jay and I have been trying to come up with a good way to embed ogg video with the new video tag and have it still work in browsers that don't support that yet. We want to show people how to set that up at the Open Video Conference. We came up with a method similar to this but hadn't finalized it yet. Anyway, Kroc Camen's Video for Everybody code is better.
There were a few things about the Video for Everybody code that I didn't like so I edited it so that it validates as HTML5 and in the interest of simplification I took out the fallbacks for "QuickTime Installed but no Flash installed" and "No QuickTime and no Flash installed." Also, the QuickTime object fallback is simplified because it assumes playback only on the iPhone.
Updated 6/3/09 (thanks Kroc!)