I'm sure someone else will soon be bit by this, and I haven't seen any definitive posts on the subject, but, if you are attempting to use avrdude to upload sketches to the new Arduino UNO (and probably the new Mega whateverthehell#theyused), the only change I needed to get avrdude working was to change the port speed from 57600 to 115200.
FWIW, if you use the BSDMakefile from the Arduino Playground, it's UPLOAD_RATE in there.
