Joshua Porter has some conjecture. He stumbled upon a survey asking iTunes' users questions like "Would you like to see what music your Friends are listening to?" Here's his take:

Apple's recommendation system lags way behind those of Last.fm and Pandora, whose services make it easy to discover new music and connect with others. By allowing people to see what their friends are playing (and not just those people on the local network), Apple will do some sorely-needed catching up.

Agreed. The fact that Apple has to do a survey to find out whether iTunes needs some sns features, is pretty sad.

q: Which iPod are you?
a: The one with friends.

Come on, Apple. Get with the program.