Still not braved it yet ! Noticed a few of your posts over on Macrumours Sneeks.
I've restored back to the official Apple 1.1.3 OS. The Jailbreak was good but I found the handset to be less reliable. The data connection would occasionally not work and the phone would require a reboot at least once per day. Maybe this happens if you have ran only a Jailbreak on a o2 tariff rather than a full unlock and activate for use with any network.
I'm not having any problems with my o2 iPhone tariff either. Everything running as it should.