Mine came back from Nokia on Thurs, working, by Fri it had locked up again, so I have to send it back to them again. So far, hardware resets make no difference, the phone reboots into a locked unresponsive state. Been onto Nokia support and I have to send it back yet again, so that will be another week or more without the phone :-(
Worse thing is, they cant tell me if they will exchange the phone for a new one as the tech repair guy has to make that decision, Im worried that all they will do is flash another firmware on and then send it back..