Talkboard by Citrix is a social whiteboard app that can be used for both work and play on the iPad. The collaborative app lets users communicate ideas with one another live as they sketch, doodle, and compose images in real-time. After someone finishes with their drawing, another can take over and edit or contribute their own ideas to the digital whiteboard.
I think this could be a very interesting and productive app! Or a very unproductive app! DRAW A BUNNY!