[Which for them means H.264, apparently][link], and no Ogg support. I’m glad to see the IE team getting on board, but I wish Ogg was a more viable option for authoring web video.
As it stands, it’s really not worth authoring two formats of video (Ogg and H.264) if you’re aiming at accommodating the most people for the least effort/space. I imagine most places will author an H.264 version and a Flash or Silverlight version, just based on usage.
[link]: http://www.zdnet.co.uk/news/desktop-apps/2010/03/17/microsoft-previews-internet-explorer-9-with-html-5-support-40088334/ “Microsoft previews Internet Explorer 9 with HTML 5 support | Desktop Apps | ZDNet UK”