Well, life just got easier (harder?). I just bought a used Roomba with a bad battery. Bought a new bat on ebay and it is fully functioning. SO, I already can control the Roomba via IR from my Mac using irTrans and iRed2. Very cool but limited control. The next step is to hook up the Arduino to the Roomba via the Roomba's serial port.
Then it looks like more control and responses from the roomba's sensors and fully autonomous as well (with bumber control and maybe converting the cliff sensors to another sensor type). Now if I can find either a used electric wheel chair or some very cheap motors I can replace the connection to the roombas wheels with the bigger motors and I should be half way there.
Roomba Brain with Arduino Controller. Then maybe OSC via iPhone to Xbee or something...
More as i collect more hardware...
Very cool.