While this was posted as a joke for April's Fools by ThinkGeek, it's actually been turned into a functioning device by an enterprising modder. Granted, it's made out of cardboard, but once he makes a more permanent case, it's going to be quite popular.
ThinkGeek showed people an iPad arcade cabinet as an April Fool's joke, but that didn't stop gamer and modder Hideyoshi Moriya to build a real one, albeit out of cardboard. This cabinet sports some interesting hardware, including an Arduino, a sort of computer that can be programmed to do things. While initially, it was thought of a joke, ThingGeek'S iCade is actually available. It costs $150. Once the iPad is docked, you can play old school games using the custom controls of the arcade cabinet.
For Moriya's cabinet, you plug the iPad into a dock. This allows you to control the software with the joystick, thanks to the Arduino micro-controller. While at first both ThinkGeek and Moriya were just joking around, there might be a real demand for this kind of thing. Look at the different types of hacks and DIY projects that we've seen this week. An iBook and a Macintosh Classic were hacked to serve as a docking station.
The only thing that remains to do is to make something more durable than a cardboard cabinet, preferably something made out of wood or Plexiglas. ThingGeek's iCade is available already, and the app will soon be on sale as well. It looks like this concept already made it into reality.