ABABAAbBAABABABABABABABABABABABABABABABABABABABABABABABABABABABABA

That's what the AVR said.

I routed the 4.7kohm resistor to pin 12 (port D6), so that the AVR-USB stack can control device reset.

I then hacked up something - with a bit of trial and error - that puts out what you see above. The first few characters are consistently buggy for reasons I can't yet figure out... I'll post the source later when I get the cruft out of it.