Reboots suck
When is Microsoft going to figure out how to roll-out patches that don't require reboots? It's hard to pitch the reliability of Win 2k3 Server when you have to reboot every couple of months. It gives the Linux nuts a reason to kick sand in your face too. Granted, it pulls my sites off the air for all of two minutes, but that's two minutes too long.
The longest I went was three and a half months on my current box, no problem. Everything still appeared healthy and I didn't need to cycle any services or anything. It would've been cool to go longer.