I upgraded from 12.04 LTS and I had a few niggles - the configs for Compiz were messed up and the AMD proprietary driver wasn't working, oh and grub got nuked.

Ultimately, blowing away the compiz configs (rm .compiz*), a dpkg --configure -a fixed the AMD driver and boot-repair from a Ubuntu LiveCD was a wonderfully simple way to redo grub.

Not painless but not particularly difficult to fix.