As I understand it, it's going to be an application built into ITunes which tracks what you're listening to and automatically shows you what all your friends are listening to. Every time somebody mentions a particular song or band, there will be a "buy" link. So if your friend writes: "just listening to Bonnie "Prince" Billy's new album, it's really starting to grow on me..." there will be a link to purchase the album (motivation + opportunity + trigger = sales). It sounds very clever to me. And if it's integrated into I Tunes, an application which millions of people already use, it'll be very successful. Unlike Facebook or Twitter or whatever, it has a very clear business plan - it doesn't need 500 million members to make money from advertising, it only needs to increase the amount of music people buy. Which it will do.