Some very surprising news has come from Scott Guthrie in a recent blog post he has made. Visual Studio 2008 and .NET 3.5 will be shipping with the source for the base class libraries. As with a lot of the recent technology coming from Microsoft, the source code is open and not hidden away.
In the past, tools like Reflector have allowed developers to see what is going on within those libraries. These tools will no longer be as necessary. This source code is being released under the Microsoft Reference License (MS-RL). It seems Microsoft has started a new trend for itself in releasing its source code.
Debugging will now become much much easier with this code being open source. In the past developers have not been able to step into any of the base class libraries. Now that the source is open for everyone to see, people are able to go in and step through this code. This should make debugging much easier and better.
I think this is great that Microsoft is releasing more source code to the general public.