Once you follow the configuration steps in Shawn's post above, you'll be able to dynamically load the debug symbols for .NET Framework libraries and step into the source code. VS 2008 will download both the symbols and source files on demand from the MSDN reference servers as you debug throughout the framework code:

Figure 1

Developer comments are included in the source files. Above you can see an example of one in the Dispose method for the Control base class.

Sometimes you'll see comments that reference a past bug/tracking number in our bug/work-item tracking database that provides additional history about a particular code decision. For example, the comment above calls out that a particular field shouldn't be nulled to maintain backwards compatibility with an older release of the framework, and points to a backwards compatibility bug that was fixed because of this.