Great documentation here - including the user forums:
http://netjuke.sourceforge.net/

but most particularly here:
http://homepage.mac.com/oddball/netjuke.html

Upside - user picks what they want to hear, can maintain playlists, browse by artist, genre, album etc.

Downside - well you'll be running apache (but your already doing that, no?) and unless you take care you may well make available to the world at large music which you ought not. For me I serve only inside a firewall and am really happy with the setup.