I just built up this circuit with a bootloaded Sanguino chip, downloaded/unzipped/moved files around per the Sanguino.cc directions, added stuff to boards.txt for -0021 and was able to upload sketches via the Uno's USB port.
Skyjumper has it now, programming with -0022, and he was even able to install an SD card shield on the UNO headers & it worked with 1 more connection, bringing a SS pin back to the shield - the other SPI pins were connected already via the ICSP or JTAG connectors.
Rx & Tx are connected via the socket for programming via Serial (0).
Serial1 goes out via RS232 driver & DB9 connector.
