Last.fm scrobbles your music aka it keeps track to what you listen. It makes charts and based on those charts, it will give you recommendations.
It also lists events, friends you are compatible with and you can check your own compatibility with others.
All you have to do is download the scrobbler and it'll list the songs you play, no matter what music player you use. It also does this for iPhone, Android, etc.
Example of charts (based on my own music, so don't laugh )
If you're interested in joining me, then join up:
Keep on listening?