Gizmodo posted about this really cool iPad app that lets you perform sophisticated 3D light painting. Check out the video and make sure to watch the machine shop animation short after the behind the scenes stuff.
We use photographic and animation techniques that were developed to draw moving 3-dimensional typography and objects with an iPad. In dark environments, we play movies on the surface of the iPad that extrude 3-d light forms as they move through the exposure. Multiple exposures with slightly different movies make up the stop-frame animation.