We have a shop of forty seats, we run 6 xserves as well as an Xraid. All of our needs are met with these machines which span from first generation to third generation servers. All run 10.3 and we've never had any problem. Nope I take that back, we had one drive failure, but it was a mirrored drive, so not so many worries.
I am not sure what your real disqualification is though? Its a BSD unix, running a series of open source services on it?
Just like everything else with Apple lately, fantastic hardware and software and a moderate price. Works for us.