Matt Parker, former Eyebeam fellow and NYC game designer extraordinaire, has just released Recurse, one of the first game's I've ever seen to use the front camera on the iPad. The object is simple -- keep your body with the green blocks and avoid the red ones. Simple to play and lightly calesthenic, it's a great nod to the physical aspects of iOS play.
(FYI -- recursion is the process of defining a function or calculating a number by the repeated application of an algorithm. Not sure what that has to do with contorting your body in public, but hey, metaphors!)