Can Duemilanove USB interface be used for data transfer/programming when the board itself is connected to an external power source? (say, USB is not powerful enough)
What are the requirements for the ground in this case? What do you have to do if your external power source is battery?
Is it possible to connect external power source when USB is already connected?
The following forum post http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1287771433 , seems to suggest the answer to the first question is "yes", but some official data source would be appreciated.