Just implemented box2d Mouse Joints in vvvv (which can also work in multitouch), so thought about sharing a small video :)
The terrain at the bottom is generated using perlin, then I built an edge chain with it. It's rendered as a mesh using a heghtfield mesh plugin (still in development, but will be fully ready soon).
Recorded with fraps, so quality is not perfect, but decent for demoing.
There's some new box2d features coming up, so will be happy to share those as well.