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.