H.264 is one of the two major HD (high definition) codices used on Internet multimedia broadcasts. The other significant HD standard is Microsofts implementation of VC-1 in Windows Media Player. Microsoft will also be making VC-1 available in Silverlight, its cross-browser, cross-platform multimedia plug-in. Novell is working with Microsoft to bring Silverlights functionality to Linux in a Mono-based project called Moonlight.
Still, H.264 seems to be pulling ahead in overall popularity. H.264 is used in Apples QuickTime Movie file format and in HDTV in the MP4 format. It supports such less common formats as M4V, M4A, Mp4v, 3gp, and 3g2. In other words, there is going to be no shortage of HD movies, shorts and so-on for your newly augmented Adobe Flash Player.
It will, however, take a while for much of that content to appear in a format that you can get at. For example, while in theory you can play Apple QuickTime Movie films in the new Flash, getting a stream to feed into say a Firefox-based Flash player is almost impossible.