Blue screen of death at an inoppertune moment - then what? If the equivalent happens in Linux you put in a live CD and get that all important presentation off of it and go on your way. Not to mention that I can install Ubuntu freshly in under and hour, windows takes several times that by the time you install 4 drivers and reboot after each one, install a half dozen apps that aren't included by default etc.

That was pretty much what sold me, I was 30 something hours into a Solidworks project that forced me to use Windows, and the machine BSOD me at 4am the day it was due. If you rely on a machine you have to have faith it will work during crunch time.