I am having the same problem with my early 2011 macbook. Here is a video showing what it looks like when it happens while working on something. This video was shot a couple days after taking it to apple. They wiped the drive and reinstalled mavericks, ran some tests and called me back saying it was in perfect working order. Even before testing it, they proposed that I would probably need to have the logic board replaced. I recommended that the computer be tested first before I go spending $600 bucks on a new logic board which will end up just failing again. Reminds me of the RROD nightmare with my xbox 360. Hope this gains popularity enough to force Apple to take action. I have a $2400 paperweight, not happy.