Well, yesterday they finally acknowledged that I have, in fact, paid my 2006 taxes...
...and sent me a check for $144 and change that they appear to believe I've overpaid.
I'm holding off on the celebration, though. Next month, I'm certain I'll receive a letter from them saying "You know that check we just sent you? We'd like it back now, kthx. With interest." Because, I don't know, they'll think i didn't properly itemize my deductions from expenses incurred while invading France or something.
I knew my taxes were complicated, but apparently they're too complicated even for the IRS to figure out.