My understanding is if the OS crashes the computer goes down with it. Applications cannot bring down everything like they can now, but system problems will still be present. Windows NT/2000 is supposed to do the same things as OS X (fully protected memory, preemptive multithreading, blah blah blah) and I've seen it crash before. But mostly because the person using it loves getting beta drivers for all his hardware. Faster but not stabler. Anyways, my understanding is that crashes will still happen, just not nearly as often or for the same reasons as before. Someone please correct me if I'm wrong.

Blizzard.