You see the black, six-pin header connector on the right side of the blue board (the Ethernet Shield)? That's the the ICSP bus in Arduino-speak. That's supposed to connect into a matching set of pins on the white Arduino board so the Ethernet shield can to its "talkin' to the interweb" thing. Do you see matching pins on the ADK board? Yeah, neither do I.
Turns out this is a bit of a problem, because the Arduino Ethernet Shield documentation states:
Arduino communicates with both the W5100 and SD card using the SPI bus (through the ICSP header).
Like I said, bit of a problem. Looks like there are exposed copper pads on the bottom of the ADK board for the ICSP connections, so I could solder in some connections if absolutely necessary. Those pads (MISO1, MOSI1, SOCK1) are clearly wired to 50,51 and 52 as described in the Arduino Mega 2560 schematics.
Time for some hand wiring...