My 2009 Mac Pro 4.1 with 2.66 Quad Nehalem, 16GB RAM, two 128GB Samsung SSDs and an EFI-flashed EVGA GTX570 2560MB having random sleep issues. Second monitor working great. First, the primary screen (Apple Cinema Display 24") goes white. Trying again, it shows my desktop (with all windows open) but NOT my cursor. I can hear the machine going to sleep, but the GPU fans stay on. The Power-LED stays on, doesen't blik or anything. Then again, white screen and so on. I made a video of it: http://www.youtube.com/watch?v=YE8G0LRQXXw I suspect the GPU being the problem. I have 10.8.2 with f02-driver installed, everything works fine.