From Interlock Rochester Wiki
Phatball is a giant trackball that wooby is building out of a bowling ball. A pressure sensor mounted under one of the supports might have a pressure sensor hooked to an arduino / mouse click button that would let you "click" the ball with sufficient pressure.
Potential uses: ultimate Katamari Damacy input device, virtual globe/google earth. I'm looking at the Penumbra OpenGL library for Clojure to make a basic Katamari clone
Basic plan: piece of plywood, with three evenly-spaced ball-bearing casters mounted at 45 degrees on wooden ramps that hold the ball. Optical mouse sensor mounted in middle.
Status: I've ordered the casters on 3/20, planning on getting 0.1 together by the end of March