http://support.apple.com/kb/HT4286 "Resolves an image corruption issue that may occur when disconnecting and reconnecting external displays while the system is running." --- I'm still having this issue after installing this update. 17" Aluminum MB Pro (Model Identifier: MacBookPro5,2), Acer 22" Monitor (AL2216W), hooked up via DVI with Apple MiniDP-DVI adapter. Happens when disconnect/reconnect, or wake up from sleep. Doesn't reproduce every single time, I'd say about 50%. Happens when using 9400m and 9600mGT.