Scott has just announced that the .NET Framework Library Source Code now available!! As Scott states: You can now browse and debug the source code for the following .NET Framework libraries:
We are in the process of adding additional framework libraries (including LINQ, WCF and Workflow) to the above list.
Note: The primary goal here is to enable developers to view source code to the underlying .NET Framework while building apps. As such, the ability to view the source to .NET is granted under a read-only reference license.
Happy hacking! :)