You can watch the Joe Belfiore keynote from Mix06 (streaming) via the following link.

http://metahost.savvislive.com/microsoft/20060321/mix_belfiore_20060321_100.asx

The whole thing is nothing but goodness so I highly encourage you to watch everything. For those of you interested in the Windows Media Center portion...

41:50 Introduction and demo of currently shipping version of Windows Media Center running on XBox 360, including Comedy Central experience featured in Online Spotlight.

54:15 Demo of Windows Media Center in Windows Vista.

1:01:15 Demo of the 'Q' Windows Media Center Podcast Client SDK Sample Windows Media Center Presentation Layer Application.

1:04:10 Demo of the NASCAR interactive experience using WinFX (WPF and WCF).

Enjoy!