Did you see the video of Dave Johnson's magnet machine the other day? He cleverly used magnetic spheres (one brand name is Buckyballs, but there are a bunch of different brands) to do all kinds of nifty moves within a machine. Eventually, I remembered posting about this marble-track toy: the Magnetix I-Coaster. It, too, uses magnetic balls to perform some unexpected maneuvers.
As you can see in the video, the magnetic aspect of the 10mm spheres comes into play at the "magnetic bridge" where the ball clings to a bar above a gap in the track. The ball also is able to roll on the outside face of a downward curve! Also, the Magnetix iCoaster uses the magnets to create an invisible elevator to raise the balls back to the top of the track. I'm not sure, but magnets may also be used for the landing area of the little jump that the ball performs.
When you look at the iCoaster and what Dave Johnson created, you start to get the sense that there are lot of cool things that could be done and the surface has just been scratched.
Here's where you can read a really complete description of the Magnetix iCoaster