I don't have the chip and haven't spent much time looking at this, but if digital pins 14 – 19 do not map to analog pins 0-5 than that doesn't seem identical to me. Also, is the USB serial port really on digital pins 8 and 9 instead of 0 and 1?
And is there somewhere (other than going through the datasheet) for information on getting Arduino code that access the registers particularly the timers and direct port io running on the sanguino? I don't have an ATmega644 so haven't' needed to bother with the datasheet but I would be happy to help people get code running on the chip if someone had some notes on mapping the equivalent ATmega168 data ports and timer registers.