I got my phone back from repair (usb port). Restored my backup I'd made before I sent it off and now get random reboots. Sometimes it'll even reboot in the middle of rebooting.

I'm going to reflash this weekend and see if it keeps doing it. If it does I guess it's back to Nokia.

Real pain in the arse. I was in the middle of a call with the police (bike stolen a few days back) when it decided to reboot, very helpful thank you.