In the end I just did a fresh install (not upgrade). I have /home on a seperate partition so had no problems. System came up with the user data intact, and the machine is happily crunching away doing a world update whilst I'm at work.
I also had problems with key mappings after the upgrade, and saw that other users had also had problems with these after upgrading.
Maybe the repair option would have worked, but with a /home partition I don't really see the advantage of an upgrade. I can re-edit my conf scripts much quicker than the extra time an upgrade takes over an install (it had deleted my net startup config anyway
Thanks for posting back!