I was just about to declare my Mountain Lion update a success when I noticed a wake-from-sleep issue (ugh). I left it plugged in last night to test the PowerNap feature. When I opened the screen, it wouldn't wake up. I pressed the power button and it restarted. I closed and opened the lid, and it appeared to work. However, when I closed it again and opened the lid about 20 minutes later (again with it plugged it), it wouldn't wake up again. Has anyone else noticed this? Update: I closed the lid and put it in my bag, thinking I'd take it to the Genius Bar at lunch. When I arrived at the office, I noticed that the fans were running and it was hot to the touch (so it never actually went to sleep). Before Mountain Lion and the SMC update, it was running fine. I attempted to reinstall the SMC update but it said it wasn't applicable for my system (I checked and I downloaded the right one).