Okay, so I know this sounds really stupid, but here it goes. I was watching the Matrix Revolutions trailer (Because I'm bored), and of course, I have to go out and get the Ultra size, so it's at HDTV resolution. Well, I end up clicking on Zoom 200%, just to see how crisp it would be and to see if it keeps a decent frame rate. Well, it ends up crashing, and I had to do the X-Windows 3-fingered salute (ALT+CTRL+Backspace) to get X working again (I tried killing it from another terminal, but mplayer just wouldn't die!)

If it helps at all, I was using X11 as my vo driver.