From their about page:
Slacker was founded to deliver personalized radio to everyone. We combine the knowledge of the nation's leading music experts from every genre and your own personal tastes to create perfect radio stations for each and every listener.
We love music, and you'll hear the difference that it makes in every Slacker station. Slacker Radio is much more than a playlist creating computer that chooses songs that are similar to each other. Our expert DJs hand-pick songs based on their extensive knowledge combined with your personal preferences. Our music library is larger than our leading competitor's by millions of songs, so you'll hear all of your favorites and a ton of new music that we know you'll love!
