My WP7 LG-E900 decided to do a factory reset last night. It locked while playing the XBox Live GEODefense game on a particular busy level I had just lost (so lots of graphic processing). The phone paused for a while then restarted and ran the first use wizard, in German. This is because it is one of the PDC units that seem, given the packaging, to have been sourced from Vodafone German.
This is the first failure I have had on the phone, not a real pain as once the phone was back running jn English it was quick to setup and sync, but 15 minutes I would rather have not spent.