Did I read that right? Yes you did. Microsoft is releasing the source code to the.Net Framework libraries. If you want the details, checkout Scott Guthrie's blog post on the topic.
... from Scott's blog
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).
You'll be able to download the .NET Framework source libraries via a standalone install (allowing you to use any text editor to browse it locally). We will also provide integrated debugging support of it within VS 2008.