At the moment I'm working on an aspect of a larger project and I'm trying to construct a tracker - something which can essentually follow a moving object. "The fish following the finger" trick you tried as a kid would be the closest idea.
So far my test setup is pretty basic. Couple of servos hooked up to a TLC5940 and a URM37 providing the distance measurement.
Over 180 degrees it takes a reading and simply chooses the closest measurement.
 with laser (everyone loves lasers right?)
Anywho, I've been searching around and I've not actually seen any examples. I know people have done something similar for nerf guns and various other turrets. Does anyone have any handy links?