For most people, the AV adapter that plugs the iPad 2 into your TV doesn't seem all that essential. Until you see this demo for the upcoming Real Racing 2 HD game.
You can mirror the iPad's display to the TV, sure, but you can also set it to act as your main screen while your iPad is a secondary screen showing the track you're racing on. You use the iPad as a big controller and watch the action on the TV. And man, does it look awesome. I think this game is gonna sell a whole lot of cables.