Those viewing your wall can then click on a track in your playlist and have it immediately stream to their computer, provided that they're also subscribed to the streaming music service. (The details are hazy on whether this is a service-independent solution. So, for example, if you're subscribed to Spotify and your friend is using Rhapsody, will your friend be able to stream that track from Rhapsody?) We'll learn details as they're revealed. In the meantime, there's the question of what impact this may have on the consumption, delivery, and marketing of music.

At one time, radio and, later, MTV, determined what would and wouldn't populate the top of the music charts. As radio's listenership has declined and MTV has become increasingly irrelevant to music fans, very little has risen to take its place. While we may have access to millions of tracks thanks to the iTunes Store, Pandora, and various music subscription services, it's difficult to choose what to listen to. Where do you go for guidance?

For many people, the answer lies in their youth--from your friends. Whether it's going to your pal's house and listening to the hip-hop CD he's just purchased, sharing an earbud with your girlfriend, or getting a text from the kid down the street about the song that closed out , we often rely on people whose taste we trust to tell us what's worth listening to.

The problem is that, up to this point, this scheme hasn't been implemented very well. Streaming music services have added social networking components, but it's been a hard sell because most people don't see the value in "renting" their music, thus making it difficult to find friends who belong to one of these services.