We have great news today for all you .Net developers. We are releasing the source code for some of the .Net Framework Libraries. Other to follow. He is the quote from Scott G.
We'll begin by offering the source code (with source file comments included) for the .NET Base Class Libraries (System, System.IO, System.Collections, System.Configuration, System.Threading, System.Net, System.Security, System.Runtime, System.Text, etc), ASP.NET (System.Web), Windows Forms (System.Windows.Forms), ADO.NET (System.Data), XML (System.Xml), and WPF (System.Windows). We'll then be adding more libraries in the months ahead (including WCF, Workflow, and LINQ). The source code will be released under the Microsoft Reference License (MS-RL).
I know folks have been decompiling these libraries for a long time but the ability to have full debug support for them is just sweet.
Releasing the Source Code for the .NET Framework Libraries - ScottGu's Blog