Well, despite a restore and also deauthorizing, reauthorizing and downloading a new free app, I'm hard pressed to say much has improved. I haven't actually put a stopwatch on it, but my backups still are taking much longer than they did before. I'm not sure when the longer times reappeared, though.
Does having specific applications installed affect backup time? I have about five pages worth installed, so I doubt I am pushing any kind of absolute limit on number of applications installed. What about having lots of applications in iTunes that aren't installed on the phone?
Edit: I did a bit of Googling tonight and found reference to Facebook being a culprit in longer backup times. The advice was to be sure to update to Facebook version 2.2, which I already had. But on a whim I deleted it from the phone and from iTunes and synced. Then I downloaded a fresh copy of Facebook and reinstalled it. So far, I think I may have hit on something. Speed has improved quite a bit. But I'll have to wait until after a day's use and then see again before I'll believe this is it. If someone else tries this, post your outcome here.
Edit 2: Never mind. I'm backing up this morning and the glacial backups have returned. I have no idea how long it will take, but the progress bar is stopped at about 5% of the distance to the finish and has been for about 10 minutes..