So first impression on rebooting into an upgrade of Ubuntu 12.04 — busted install. Unity would not start up, I killed lightdm and restarted it, and I immediately notice that firefox has missing png for some of the tab buttons.
Presently I’m repeating:
$ apt-get autoclean $ dpkg --clear-avail $ apt-get update $ apt-get -f install $ apt-get autoremove
And this appears to be doing a good job of finding and removing corrupted /var/…/dpkg package files and fixing my install.