The Slides and Videos from this years Game Developers Conference have been added to the Microsoft Downloads site.
Networking with the XNA Framework
Speaker: Shawn Hargreaves
Understanding XNA Framework Performance
CLR Performance
Speaker: Frank Savage
Extending the Content Pipeline
Advanced Debugging with Managed Code
Speaker: Matthew Picioccio
XNA Game Studio 2.0 for Xbox LIVE Arcade
Speaker: Mitch Walker