In case you missed it, Microsoft shipped XNA Game Studio Express 1.0 last week. XNA provides a rich .NET based framework for building games, and supports development using C# and Visual Studio. The games you build with it can then be run on both Windows clients, and XBOX 360 consoles.
XNA relies on a version of the .NET Compact Framework CLR that we ported to run on PowerPC chips (the XBOX 360 ships with a 3-core PowerPC CPU). For a killer demo that will impress your friends, install XNA Express, load up the built-in "SpaceWar" C# starter kit template, customize it, deploy it to the XBOX 360, run it and dazzle them with the graphics, and then set a breakpoint within your C# code in Visual Studio and show hitting the breakpoint and stepping through it in a live debug session against the XBOX 360 as you are playing the game. Pretty cool.
You can download XNA for free, and learn more about it on the MSDN XNA web-site. Included on the MSDN XNA site are a number of nice Channel9 videos that you can watch here to quickly get up to speed on the project. I also found the www.xnadevelopment.com site very useful (it contains a number of good step-by-step getting started tutorials - like this one).
If you are looking to have some fun this holiday season, try writing a cool game using .NET.
Hope this helps,