Video stopped working.

About an hour ago, I noticed my video wasn't working properly. It takes files literally a minute or more to launch, and they freeze randomly in the middle of playing for 10+ seconds at a time; sometimes audio continues, sometimes not. I know it isn't a slow hardware problem; I'm running the 27" 2010 Core i7 iMac.

This happens EVERYWHERE, by the way; iTunes, QT, VLC, Movist, Mplayer, even in QuickTime 7 & MPEG Streamclip!

Any ideas? Anyone else having a similar problems? I can't even think of anything I've done differently for this to suddenly go bad on me. It was working fine yesterday and this morning (and I was on Lion DP4 then, too).

Update: it even happens with Flash & Silverlight video.

Update edit: Okay, so now System Preferences is taking forever to load. Seems like it's more than just video. I think I may just go back to SL. This is a nightmare.