I'll be honest, when it comes to updating my system I'm a nervous nelly. I spend the entire time chewing my fingernails and praying that the progress bar keeps moving and I don't lose everything in a blink of the screen. Here's my idea, I know its a bit 'ambitious':
During the upgrade process, give the user the user the option to backup their system such that it can be restored if something goes wrong. Yes, they probably should've done it before starting, but make it easy for them and really walk them through it. Then (and here's the ambitious part) let then upload it to an Ubuntu server under the condition that it will only be there for like a day or so (give them a user name/password, etc to make it secure). Then if something goes horribly wrong, they can re install fresh and do a "Restore from Ubuntu Repository" and get back to where they were.
I know there are huge holes all over the place in that idea, but I'm just throwing it out there for thought. For me personally, like I mentioned, updating from one version to another is just the most gut wrenching thing.
Thanks!!