Ok, I've reflashed the phone with the latest firmware, installed the maemo 5 update, installed a number of apps, and have NOT enabled the extras-dev repo. I even installed titan kernel as advised above.

I then noticed it restarting itself again, the bootreason was sw_rst, and the dmesg log looks a little more interesting this time. It seems to continually be "disabling unused clock" for different variables, before it says "Bootup reason: sw_rst" and from that point onwards it looks normal

"cat dmesg" output has been attached as "log2.txt"
"cat /var/lib/dsme/stats/*" as been attached as "dsmestats.txt"

Any help is appreciated - otherwise i might return the phone for warranty repair and hope to get a new one