I'm kinda late on this but arstechnica reports that "Microsoft has opened the source code to the .NET Framework libraries under a read-only reference license. Developers who want to check out the source code need only upgrade to the newly released Visual Studio 2008 to gain access to it."
This is something I've always dreamed about -- learning by a large software firm's example. I can remember how disappointed I was during the first dotcom when companies would go down and take their source code and website designs with them. Woudln't it have been amazing if they would have donated their site templates to OSWD.org? As for the code, I realized the other year after looking at my own dotcom code, that the styles were probably pretty bad and not so good to learn from.
Check out Scott Gu's blog entry for more information on the libraries that are being opened.