My sense is that there is more than one issue here since peoples experiences and set ups seem to differ. I have 2006 MBP + ACD and have experienced these freezes intermittently for some months on SL (freeze of screens except for mouse, but sometime with the screens just going black and everything freezing.) I had hoped that Lion would cure this but it seemed to make it worse so I was getting 2 or 3 a day. In my case it did not seem to be particularly video related and could happen anytime and sometimes seemed to be brought about by a mis-keying. I followed nanofunks post and external links on this and installed Flash 11 beta and it does seem to have made a difference. In 3 days Ive just had one freeze when I had a lot of QT windows open, but this time I got an automatic restart as a result, which Id never got before even though Id set the Energy Saver preference for this. Not suggesting that this will solve everyones problem, but so far the Flash 11 beta seems to have done it for me.