pins 0 and 1 are basically echoing the USB serial stream, so anything sent or read by Serial.read() and Serial.write() will also work with these pins.
I used them yesterday to connect a BlueSMiRF module to my Duemilanove... these modules are made to connect to the 6 pin headers on the Pros and Lillypads, but the Duemilanoves have USB jacks instead of headers, so I used the 0 and 1 pins to connect the module through an overly complicated protoboard kludge, which looks horrible and beautiful at the same time ;D