Much of the work that Microsoft's internal IT department does is "early adopter" - we use our own systems to make sure that the products we release have been as thoroughly tested as possible in a production environment before being put into the marketplace. Obviously, the Microsoft environment is somewhat different to that of most enterprises, for example almost everyone has full control over their own machine and there are many, many people who are (or think they are!) experts. But we learn a lot from this "dogfooding" process, and we also make the way we implement and manage our systems available for IT Pros around the world to study.
If you want to see how Microsoft does "IT", check out the TechNet area here.
Source:→ TechNet Blogs