I don't get it.
I don't use it and can't really understand why anyone does. It's just a massive marketing tool. Where is the actual functionality that I want that should hook me to their service? Ultimately it is designed around recommendations, which it does in various ways, which would be fine if it provided some unique or valuable functionality other than this.
Hey! Let's all sign up to a big database that monitors our music tastes and listening habits! That way, we can all be told what we should be listening to by our record label overlords! Yeah! It'll be great! We'll never have to think for ourselves again!
As we continue to allow ourselves to be profiled based on our search, music, tv, movie, gaming, and other tastes and habits we are slowly killing off the field of entertainment journalism. Trend setters will go away, and we'll find ourselves locked on to a set of rails where we only ever see more of the same because there is nobody to suggest otherwise.
Mark my words...