This is very cool -- Beautiful Modeler is a software tool used between an iPad and a MacBook above to gesturally sculpt a 3D model using the iPad's touchscreen. As you can see, the iPad works as a controller for the app running on the MacBook, and not only is touchscreen information passed on to the 3D modeling program (I like that multitouch works as well, so you can mold five different points in the sculpture at once), but accelerometer information is also passed across, so tilting the iPad around also tilts the onscreen view.
The source code for the project is readily available on the site, and while the gesture control currently hooks up to just one kind of form modeling, technically you could hook this up to any 3D sculpting program and sculpt away. The app even outputs a special 3D format that can be connected directly into a 3D printer, so you can make a form with the iPad and the modeling app, and then turn it into a real 3D object by printing it out.
Very impressive. Even Apple probably never envisioned using the iPad as this kind of interface, but that's what happens when you have such a relatively cheap and powerful touchscreen computer available to almost anyone.