Plenty of times. Usually, its a BIOS setting or bad RAM stick, both easy to diagnose and fix.
The good thing about spending most of my time on Linux is that I no longer have to try to help people fix that, I can just say 'I don't know anything about Windows any more'.
Not really. Sure, you can make Windows run like crap by installing every piece of malware under the sun, but hey, thats true for any OS. And I've yet to see a piece of malware actually cause a BSOD in the NT 6.1 (Vista/7/8) Kernel.