My 15" MBP I7 2,66ghz has got the same issue with garbled graphics.
BUT, Its happening more often when I work in Photoshop, Bridge or Capture One.
I has happend in Safari a couple of times and when I got Safari running in the background (no windows open).
When I change user from within one account the graphics garble.
When watching a movie in Quicktime I changed the brightness and bang, kernel panic (Safari not running and nothing but the powercord connected).
I put some screenshots here (sometimes they come out black):
http://www.klackenstam.com/dropbox/garbled_graphics
Im not dropping Safari but would love to drop Flash....