When I first started, this diagram and info was being circulated, and it was pretty darned impressive. I thought it was appropriate to resurface it as questions about deployment scenarios has come up a lot lately. Here are some highlights from what Microsoft's very own developer division is doing:
Here is a link to the latest stats off of Brian Harry's blog from February 2007: http://blogs.msdn.com/bharry/archive/2007/02/08/february-devdiv-dogfood-statistics.aspx