We use a couple of Xserves at my work, and they're gr8 at what they do: File/Print services, Mail server.
By chance I was able to get (very cheap) a second hand Xserve from a company which made the switch to the dark side. Didn't know what to do with it really, as I already own a couple of Macs, but I just wanted to have one. 🙂
But, OMG... WHAT A NOISE
I knew the fans were loud, hearing them at work, but once one of these is turned on in your peacefull little living room.... oef!
Fun to have, but a headache to switch on! 😀