Non-flame question here: what does running Mac OS as a server buy you?

I love my apple hardware and depend on my mbp as my primary computing device, but don't see the appeal of mac os X as a server environment. The things that make the mac great (for me) don't add value -- and in fact get in the way. I'm much much happier using Linux on my servers and much much happier NOT using it on my day-to-day machine.

I can imagine there could be some specialized cases in which running services on the mac make sense but I am astonished there are enough that macminicolo can make a business of it (and congrats to them for this by the way!). I assume this is a failure of imagination on my part, thus my question