"Debugger Canvas is a new user experience for the debugger in Visual Studio Ultimate. It pulls together the code you’re exploring onto a single pan-and-zoom display. As you hit breakpoints or step into code, Debugger Canvas shows just the methods that you’re debugging, with call lines and local variables, to help you see the bigger picture."
Be sure to watch the video, because the description doesn't do it justice.
A few months ago, I had to update a legacy app that seemed to defy our ability to follow the program flow. It took me an entire afternoon to whiteboard the various method calls. Had I had this tool then, I probably could have had it figured out in minutes instead of hours.
I will be the first to admit that I drink deeply from the Microsoft Kool-Aid well, but gosh darnit it's stuff like this that makes me happy to be a .NET programmer.