Been using this site for a while now and I'd thoroughly recommend it
Set yourself up a profile and start 'scrobbling' that means using your music player, be it i tunes, windows media player etc to refer what you listen to, to the site . It learns your tastes and compares you to other listeners, which gives you access to their music, and lets you hear new stuff you might be interested in
Its not a file sharing site , but I have found a wealth of new music on it from like minded peeps.
You can even start up a group like a Ribnet group of friends and share stuff that way .. there are some tracks free, but mostly you'll have to buy through I tunes or the likes, but the best bit is you can play in real time someone else scrobbled tracks or 'radio' and hear a full track, so you'll know if you really want to buy it ,. or the album it came from, rather than spending loads on stuff you thought you might like
Also you can play 'radios' from your fave artists, which also brings in similar tracks from others of a similar genre
I think its fab !