It's been an eventful day.
I backed up my home folder (which contains gigabytes of data due to my
involvement with the Replicant project) and reinstalled the system. I used
text mode, but this booted into a textual environment, and even after
installing XFCE nothing worked.
So I reinstalled graphically, and got the system working. But the backup sure
is taking a long time to do anything...and I'm concerned I might have to
reinstall due to a failed attempt at installing XFCE without running sudo
apt-get update.
I backed up the most important of my files in a second foolproof location, so
they're okay. But I really hope the backup starts to respond.