Any time I get these they come with a bushel of IOAccelerator errors; I'm fairly sure (in my case, at least) it's a problem buried somewhere in the video decoder stack.

I can reproduce it pretty reliably by previewing a bunch of videos in Messages, and quitting the app usually solves it.

Edit: I use a 13" MBP, so that rules out most popular theories e.g. problems with the discrete GPU or graphics switching.