Met with a Genius today because I've been experiencing the same issues that many of you have noted where my 11" air will sometimes "shut down" if I leave it closed for more than a few minutes. I have to hold the power button and then it boots, and chrome tells me that it suffered a crash. The Genius told me that this is a known issue among airs which is rooted to more recent versions of flash (I'm running 10.2.156 according to whatismyflash.com). He promised that they are working on a fix, which was good to hear. I believe it simply because this is a new issue for me (i.e. it may well have been introduced after I upgraded flash), and it would explain why the problem is intermittent (Sometimes I close the lid with open browsers that have flash, sometimes I don't.) TL;DR - Apple knows that the airs instant start is crashing on occasion, they say it is the fault of flash, and they're working on a patch.