When I first received my N95 from T-Mobile I found it kept on rebooting/restarting.
I eventually called up T-Mobile but they hadn't heard of this issue before and organised a replacement.
I've since discovered after several restarts (probably +/- 10 times) I got a message saying something like "Interactive Update Complete" or it might have been "Multimedia Update Complete". Needless to say, after receiving this message it rebooted one last time and have since not had the same problem.
Just thought I'd post this here in case anyone else comes across the same problem.