The last three all keep waking up from sleep mode with a Wake reason of OHC2. Apparently this has something to do with the USB bus. Only problem is I never have my USB devices (external hard drive and mouse) plugged in when it happens. It's happened most of the time when I have it in my backpack. When I open my backpack to take it out it is as hot as a lump of coal with the fans going full blast. Open the screen and its black. I have to do a hard shut down. Reformatting and reinstalling the OS does not fix it. Resetting the SMC and PRAM does not fix it. Apple engineering is apparently aware of the issue so I have faith they will get this corrected soon. They have stated not all machines are affected. Let's hope this one is the one I get to keep for good.