ThinkGeek posted an iPad arcade cabinet as an April Fool's joke this past year, but gamer Hideyoshi Moriya actually did build just such a cabinet out of cardboard and hardware -- you plug the iPad into a dock, and then you can control software with the joystick and buttons via an Arduino board. You can see a full video of the device running (along with some cute puppies) after the jump below.
ThinkGeek was only kidding, and Moriya is just joking around, but there is definitely a viable demand for something like this. Sure, the cabinet form built out of cardboard is totally a prototype, but a little stand that you could just plug the iPad into and then control arcade games with buttons and a joystick? That thing would sell like hotcakes.