Here's a nifty little slideshow of my Mac screen from a few minutes ago while the compositing engine went haywire. Basically, I went to lunch, came back and when I moved the mouse to get rid of the screensaver I was getting some really nice visual effects. Maybe I should have taken a movie because there was some nice animation going on too.
Fortunately, a reboot corrected the problem.
Cheers.

Wow. That's pretty nutso.