ScottGu just posted info on something our team has been working on in conjunction with Shawn Burke (NDP) and the Windows debugging team. When VS2008 releases, people will be able to debug into the .NEt framework libraries. We will be providing full source and symbols to the VS debugger through a web server.
I think this is a great stride forward for the diagnosability of solutions built on the .Net framework - and Shawn can take a bow as primary driver. See details at the following links