Well that's my main machine upgraded, to Ubuntu 12.10 64 bit.

It was a little fraught. After installing (to my Lenovo ideacenter) it
failed to recreate Grub properly. When I rebooted the upgraded machine I
got a very forbidding Grub Repair> prompt, and no clues. So not only no
Ubuntu, also no Windows (it's a dual-boot) and no way back. Trying to
load Precise back over the top didn't work either - the live CD just
stopped after the first screen or two.

Thanks to having other computers around I was able to google for some
help. Managed to learn a little bit about the grub repair prompt, a very
minimal command line, and played about with changing some settings,
moving some files which appeared to have been misplaced, and ended up
with a very mythological error message along the lines of "Invalid Arch
independent ELF magic".

Never been much good with a magic wand, so I abandoned that and went
looking for Boot-Repair instead. I was able to boot the Quantal Live
DVD, and managed to install and use Boot-Repair from there. And it
worked, recreated my boot record, identified Quantal and Windows, and
some other options, and everything was in place once more. Phew.

Not the sort of thing, I'm afraid, that a newbie would want to have to
cope with, and that invariably holds linux back in geek-land.

Anyway, now it's to play with the latest version, reinstall all my apps,
and see what's new!