Simple question, how often do you guys restart your servers?

I've worked places where we never restarted them for years (short of a hardware failure) to places that had us remote in on the weekend and bring 30 servers down/up every saturday.

Is there any "best practices" whatsoever concerning this?

The odd thing I've seen is the places I worked where the majority of servers were windows boxes were the same ones that never wanted them restarted. While a place I worked that was largely comprised of *nix / i-series machines wanted them restarted weekly.