You don't run into them very often and you rarely see them in people's apartments, but they are GREAT. Aside from being cheap and a little bit of a pain in the ass to mount (you need to put a small hook in your ceiling), they shed the most beautiful and romantic light AND just wind up a party.
We recommend at least a 12" inch ball (go bigger!) with an battery charged motor to turn it; all of which will hang from a hook in your ceiling. The light that you shine on it is very important, and you need a pinspot light that you can either hang on the wall or rest on a table in the corner and shine up at the ball. All of this can be seen here at Chauvet, and purchased in many places. We found good prices at Canal Hi-Fi ($55 for whole kit). MGR