As announced earlier by Scott Gu, the source code for most of the namespaces in the .NET framework is available. This means that you can now step into the framework source code while debugging your applications and see its actual implementation. I had a chance to play around with this few weeks ago (thanks Shawn for sharing the setup instructions). There were few delays while debugging because of framework source code download over internet but otherwise, it was pretty smooth and neat. As the title of this blog says, the purpose of this source code release is more for debugging and seeing the code for better understanding of how the whole things works.
Follow the detailed setup instructions and see it for yourself.