This story is about my Macbook Air. In January I'd had enough of Apple and Renaissance mucking me about, so gave them another week to respond, they didn't so I filed the dispute. I also purchased a new 15 inch Macbook Pro to use in the mean time. Got it home, and it started exhibiting problems too: http://vimeo.com/2911394
Apple said to switch the power settings to "high performance" and leave them there. Basically I think this forces it to use one of the video cards and not the other. Since then it hasn't shown the problem, but the battery doesn't last as long...