I posted a question about a lemon Mac a while back. I think I have it fixed, but was curious if anybody else has had the same problem. http://forums.macrumors.com/showthread.php?s=&threadid=27736&highlight=lemon I ran the apple Hardware Diagnosis tool for 24 hrs in loop mode and it never turned up an error. But on occasion the machine would still sleep or shut down on its own. Took a visit to Tekserve where they could find no problem either. (I didn't bring in the monitor) Finally I was paying attention when it happened, and I noticed that the power light on my Cinema Display would light up like it had been pushed, it would stay on for about 5 seconds and then the machine would shut down. It was the exact same as if I had pushed the button to turn the machine off. I think I simply had a bad switch on my monitor. Quick search of the Apple support site. Found out how to disable the switch and I disabled it. Hopefully my machine gremlin is now gone. I have a 20 inch Cinema display. Anybody had issues with the power switch on the Cinema Display being overly touchy?