Like you I am encountering the same issues with my Macbook after upgrading to 10.8.2, at least that's what I hope. When you encounter a situation like this, does the macbine stop responding and do you need to hold down the power button to reset the machine?
I purchased a Retina Macbook in early August and in early September the LG screen started displaying the image retention issue. They just replaced the screen to a Samsung last Monday and since then I have formatted the drive and reinstalled everything from scratch. Since then I have on several occasions encountered a situation where the machine stops responding and requires a hard reset by holding down the power button for 5 seconds.
I have tried the hardware diagnostics but it stated that everything was ok after the extensive test, had to leave the Macbook turned on overnight.
My first thought was that the technicians that did the replacement of the display might have damaged or did something to the hardware when they opened it up. But now after checking the console logs, searching online and seeing other people encountering a similar issue, I have come to believe that it is 10.8.2 that is causing the OS to freeze, and in my opinion it has something to do with the switching of the graphics cards.
I doubt it has anything to do with overheating or running too many applications at the same time as the problem has occured randomly, regardless of whether the machine had just been turned on, running for several hours, only Safari is turned on or several virtual machines are running.