Inside the recently released Thunderbolt Display from Apple is a fairly complete computer, including several controllers and other hardware trappings. The included Ethernet port on the rear of the display is not simply a passthrough, but requires a bona fide entry of its MAC address into NetDB. Yes, the display has a MAC address. Then again, doesn't your refrigerator?
This cost me 1+ hour this morning and an actual call to AppleCare, so hopefully this post can save others some headache.
ps For this interested, here are some teardown pics on the display: