I had another issue after the random restarts, all of a sudden i couldn't wake my display with the power button, its was as it the phone was totally dead! As u cant pop out the battery i saw the only thing to do was press and hold the power button, after 30 seconds still nothing! So left it, a minute later it vibrated, then a large white exclamation mark in the middle of the screen appeared with a black background, it stayed on this white exclamation mark for a good minute, then it restarted itself and came back to life, that did it for me, clearly there's an issue with the handset so i rang O2 and arranged for it to be replaced within the 28day fault replace policy.. I had my replacement arrive next day, currently using it for 2 days with no restarts.
On another note, i logged a support ticket with HTC and had a poor response from their tech support, so I complained on HTC's forum, next thing a HTC manager rings me apologising, couldn't do enough for me, really appreciated the phone call so have say, fair play there HTC, even though ive had the phone replaced he wanted to make sure all was ok, which for now, it is.. Just installed all my apps and games and will wait and see if it restarts itself again!