Post one bug, and everyone demands you post another even more frustrating one. Our bad, should have had this up already. Seems iPhone 3.1 users, mostly iPhone 3G users from what we can make out, are experiencing random freezes and complete shutdowns of their iPhones, and nothing, not reboots, not restores are fixing it.
TiPb did hear a few accounts of freezes during the 3.1 beta on all versions of the iPhone, but that's the point of betas -- to identify and fix bugs before the software goes primetime.
Seemingly random, intermittent bugs, however, can be some of the toughest to figure out, especially for users, so if you're suffering from frozen or shut-down iPhones, let us know which device, and any pertinent details like clean 3.1 install, restore from backup, etc. and if you've stumbled onto any fixes of the more-than-temporary variety, please do share.