Google Chrome is dropping support for the video codec H.264. Kinda feels like an Apple vs. Google pissing match as H.264 is so heavily used by Apple and WebM was developed by Google.
For HTML5 video, this is how it seems like it shakes down to me:
H.264 - Chrome, Safari, Mobile Safari
Ogg Theora - Firefox, Opera
WebM - Chrome, Firefox, Opera, IE 9
H.264 - Safari, Mobile Safari
Still only need to provide in two formats to get pretty good coverage. If Safari can get on the WebM bandwagon we'd be all set, but don't hold in your farts till that happens.