Been having this problem since i bought my 11" Air over the summer. Same exact thing, shows in system profiler, restart fixes it temporarily and then it zonks out again after prolonged sleep. It worked for a bit during one of the system updates, but is dead again.
Just brought it into apple store finally to beat the rush after Xmas. So far they can sort of replicate it, but nothing definite. They're going to reinstall Mountain Lion from scratch and see if that helps. I did try this in the past, but it was Lion and then immediately upgraded to Mountain Lion. So I'm somewhat hopeful, but not really.