I've noticed this today - my entire system froze up solid, clock is frozen, nothing responds to clicks and key presses, and my time machine animation stopped going. While repartitioning my boot drive. I also had iTunes open, which happily kept on playing music. How does iTunes manage to keep playing media if the entire OS is frozen up solid? No other OS X media player I've seen can do this, and I'd love to know how this is possible.