Map Cruncher is a secret little project that Microsoft Research has been working with the Virtual Earth team. The basic idea is that you can take any map in PDF format and overlay onto a Virtual Earth map. The benefit being that you can have your own specific map with the cool Virtual Earth draggable functionality, double click to zoom in, pan, etc. As an example, I can take a PDF map of Disneyland and overlay it onto a Virtual Earth map. So, while I'm flying around Virtual Earth I can also explore the Disneyland park map. You can read about it here:

http://www.microsoft.com/presspass/features/2006/may06/05-16MapCruncher.mspx.