i had nothing running and i closed the lid for it to go into sleep, then i put it in it's case (generic neoprene apple sleeve with a zipper knockoff from ebay) i goto class. at the end of class i notice that my bookbag is pretty warm. i pull out my macbook sleeve to hear my macbook with the fan all the way up. apparently it never went to sleep and was going to overheat eventually it wouldn't turn on the screen, the white light on the edge was solid. so i had to push down the power button till it turned off. when i turned it on, it had a bluescreen for about 30 seconds, then finally the apple showed up my battery was at about 3 hours when i went to class. i was in class for an hour and 15mins. now the battery says 16 minutes left. holy shit, it was like that for the whole class. as far as i can tell, it didn't do any damage. i hope not why would it not go into sleep mode ?