I have been using it for 5 years now and it has helped me stumble upon some amazing artists. It used to be among the first websites that would log your library as you played a song and make suggestions for similar artists.
Their radio used to be free, so you could listen to new artists (full songs!) before you bought anything. Pretty great system.
Nowadays I just use it to keep track of what I have listened to in the past, so I can come back to artists I would otherwise forget.