There are some serious issues with windows in teh data center. First and foremost is the monthy reboots I need to do for windows patches and the like. Now while one server might not seem like an issue the fact I have 40 servers with different windows and dependancies and you get a mess everymonth. Its hard enough to keep up with things. Throw in things like like the wonderful tendancy MS patches and, more often, service packs to break some functionality I depend on inorder to fix a vulnerabiltiy I cant leave open and you see why UNIX guys love their flavor.
With *nix systems, 90% of the time the patch on the fly without a reboot. the other 10 breaks up to about half the time I dont need the patch (either does not apply or I have a real time work around), or I have to up and take a reboot. It is a more stable platform than windows (but I have not yet touched 2003). And a much nicer box on system resources..
I've been using 2003 for the last year and a half. You still have to reboot, and patches can still mess up your system. The only shockingly pleasant surprise I had going from w2K AS was that IIS 6 is FAR better than IIS 5 (once you go through the troublesome migration). It actually has abilities that other servers have had for years. Welcome to new new millennium, Microsoft!