Check-out this awesome LED persistence of vision project some guy made from leftover junk in his parts box. The video (inside the post) is worth a million words.
This project features a total of 9 slip rings to provide power to the various spinning elements in the project. The effect once it gets going is pretty cool. A minute or two into the video there are some patterns which are very interesting.
Does that make you want to grab a microcontroller, a bunch of LEDs and get building? 🙂