I just updated to 10.8.5 on Saturday afternoon. I have a late '11 cMBP 15". I didn't use it at all Sunday but this morning when I opened it, the display was noisy and garbled and it locked up. Shut it down (pressing power) and then started it back. Told it not to reopen anything any apps, and then the first app I opened, the video went noisy again and it kernel paniced. Rebooted again and it's been OK so far.
EDIT - opened NetNewsWire and then it crashed again. After I enter my filevault password it just freezed - won't boot to the desktop, just grey. Reset PRAM and SMC. Safe mode and recovery just go to black screen - but the backlight is on and the apple on the cover is lit. Filevault password screen has blue horizontal lines and a blue tint to it.
EDIT 2 - later in the evening it started working again. Installed gfxCardStatus to either keep it in integrated mode or discrete so that I could troubleshoot. Does break if I run a game, but seems on in general usage - either way I was able to update my TimeMachine backup!
Wondering if it's a graphics driver/firmware change in the update and if Mavericks will fix it.