I have a Spotify Premium account and i'm addicted. Find just about anything I want, make playlists, then listen to them online or offline... Go to any computer and my playlists are updated. It's awesome. Also it streams at 320 if high speed is selected.
Don't mess with the free version beyond just checking out the interface. The advertising will turn you off.
It's cool to see it start to integrate ... but, I bought a Boxee and returned it. Found it cumbersome and kinda..well...stupid;
Love it on my iPhone. Listen to music and then when I call comes in it dims the audio and I press the headphones to answer. After the call is over the music comes back on.
The playlists I have set to Offline play even in the car