SORRY FOR THE LENGTHY POST! the first day i got the phone i rooted it. ive always been a fan of the auto killer app which manages the memory and requires root. my phone has not shut it self off once in the month ive had this. i believe the cpu combined with the ram getting over loaded from keeping too many apps in the background could be the cause. of course i am by no means an expert (so my explanation for this could be wrong for the shutting off) but i love the phone and want other people who have it be able to enjoy it too. so give autokiller a try and try the optimum setting and see how things run. there is an option in development to set the amount of apps to keep in the background to 4 but i thought it wasnt doing a good enough job.