(http://i55.tinypic.com/15h0tae.jpg)
Not too long ago, Microsoft released an extension for Google Chrome which enabled H.264 HTML5 video playback. Now Google has returned the favor by offering a WebM plug-in for Internet Explorer 9 users. In a move which we can only describe as oozing with self-confidence, Google points out that there are some known issues -- visit this page (http://www.webmproject.org/ie/#known_issues), and revel in its blankness.
If you plan on using IE9 but don't want to miss out on all the WebM videos which are popping up, download (http://tools.google.com/dlpage/webmmf) and install the plug-in now. The plug-in only works on Vista and Windows 7, but conveniently the same is true for IE9.