The new iTunes automatically creates playlists based on your own music collection. After selecting a number, you need to press the 'genius' button and then iTunes will automatically select similar songs. You can also give Genius the command to recommend music you don't own yet. Then you can buy those.
Future Vision by Erwin Van Lun on this article
This is how music coaching brands are brought to life. They’re specialists in all kinds of music ever created and can make recommendations. Soon iTunes will look at you literally (!), gauge your mood, and start the music. No whining about buying, but of course you do have to pay for this added value. And if you’re truly touched, iTunes will be able to recommend a concert. This is how iTunes will become a music buddy that travels everywhere with you.