See Brian Harry's blog to understand the scope of our Team Foundation Server deployment. The image on his blog links to a Microsoft Visio diagram. If you don't have Visio, you can download the Visio Viewer or a 30-day trial version of Visio 2003.
Given how much I talk about our internal "dogfooding" of TFS on this blog, I thought you might be interested in seeing a diagram of what our internal deployment actually looks like. This diagram was put together by our IT department a couple of weeks ago. It shows the basic network topology, regions we have servers and the number and purpose of various servers. I don't even know what all of them are but I'll point out some highlights.