Garbage out!
I thought the backup that I was running was taking a long time. I even wondered if I'd mistakenly connected the external hard drive by USB (belgian only has USB 1.1) rather than FireWire. Checking on things, /home was around 47G. My reaction was, I have 47G of stuff?!? Sometime this morning the backup stalled.
In looking things over, the .Trash directory where allegedly deleted files go was not empty. It's not that I hadn't emptied the trash. I did that right before starting the backup, or so I thought. But evidently the actions I took only made it look like it had been emptied. And evidently this deceit had been going on for some time. After really deleting the files, there's only about 14G to back up. That's much more reasonable.
The backup will still take a while and I don't expect to be installing Fedora until tomorrow night at the earliest, but now I have one more reason to do so.