This thing's very cool:
http://www.audioscrobbler.com/ Basically you install a plugin into your media player of choice (the protocol's fairly simple, and I reckon it wouldn't be hard at all to write one for jukebox systems) and it records the songs you play (all done over HTTP); it then compiles a personal chart and (here's the clever bit) using some kind of inference technique works out who else on the system has similar taste to you - using that it then makes recommendations of stuff to listen to.
Also, in conjunction with
http://www.last.fm it creates a custom radio stream of your music plus recommendations! Nifty. (It's like LJ in that a free account is pretty full-featured, but you can pay for the extras, and it's all GPLed stuff - it grew out of someone at Southampton's final year compsci project)
Quite a lot of fun to see what other people are listening to, as well. This is me at work:
http://www.audioscrobbler.com/user/covertmusic/ - for example.
Anyone else interested?