I think the main problem so far has been with people (like me) who don't have enough space for the update. The install will just fail / crash / whatever and leave you in a partly-installed, broken state, often with no clear indication of what just happened or what you should do now. And since it can run out of space at different places in the install process, the failure can look quite different...

If your install fails, and it says (or you suspect) that there's not enough space, hunt around and delete / move stuff (like the demo videos, music, etc, documentation pdf files under MyDocs..., also as root, "apt-get clean" can give you some space) and then gain root and type "apt-get -f install" to see if you can carry on installing.

If you get kicked offline, and you can't get back on, and your install fails, you could be in big trouble... don't reboot! Anyone have any ideas how to get back online?