This is kind of cool.
I am playing around with the Last.FM music service.
Among the many things it does, is that It 'watches' everything you play with iTunes to figure out your music tastes. And then with that, Last.FM recommends music that you might like.
What caught my eye is the first use of the famous 'long tail' graph as a User Interface element. You can drag the vertical bar right and left to affect whether the recommended music is more in the popular or obscure range of possibilities. Cute!