I'm having the same GPS issues. If you put it on high accuracy, it can't find the GPS. Also I've now twice seen a screen that tells me there's a new Sim card in the phone and I need to restart, so I do, and it actually restarts, no power down hang. Don't know if that'll be indicative of anything. Just wanted to throw that out there. Clean flash of 3.1+
I've been having this same issue. Instead of rebooting, back out of all of them (in my case there were like.. 4 messages of the same thing) and your sim should just re-find itself, for lack of better word.