Should I disconnect the FTDI and ICSP power supply pins via a device like the NDT2955 every time the on-board power supply is also supplying power?
3) It is VERY RARELY a good idea to "back-feed" anything, whether there is a spec or not. And I'm sure there is a specific prohibition for USB.
If I wanted to power only from the AC adapter but still be able to program via USB -- I could remove the LM358, NDT2995 and FDN340P from the circuit correct? Everything else would remain in this schematic, right?http://arduino.cc/en/uploads/Main/arduino-mega-schematic.pdf