I work for NASA; almost everyone in our group has Mac OS X on our desktops and Linux in the server room.
OS X on the desktop and Linux on the servers… Ah, what a nice place that must be to work. Luckily, in the very near future, there will be far more environments with this type of setup. I personally belive it’s going to be Linux with OS X-type functionality on the desktop, but this difference is unimportant. The point is it’ll be open-source driven OSs on both the client and server side. It’s coming.