Oak, I think you should write a book. The wheel was actually centered all along. I just seem to have uncooperative brakes, which is odd as they were recently adjusted.

The brake isn't rubbing anymore, but it's certainly off-center. (I can comfortably get my thumbnail between the rim and the brake on one side, and can barely do so on the other.) If the brake refuses to center, the next step is to loosen the nut, center the brake, then tighten it, yes? The nut in question is the one I'm not sure about. Logic would seem to dictate it's the one on the "back" of the brake, in the center (on that little cross-piece between the seat stays.) Am I correct?