Twitter DJ leverages Twitter as a human-powered recommendation channel. It was built by the guys at Foxytunes (which btw is a very slick little browser extension) and I was asked to be one of their “featured DJs”.
In their own words...
FoxyTunes Twitter DJ is a Twitter channel with music recommendations from a selected group of "FoxyTunes DJs".
Also, it allows all Twitter users to share their favorite songs with the community.
How do I post songs?
1. Add FoxyTunesDJ as your Twitter friend
2. Wait for a few moments until FoxyTunesDJ adds you back as a friend
3. Use TwittyTunes to post music to Twitter, prefixing it with "@FoxyTunesDJ". All music twits will appear right here on this page (http://www.foxytunes.com/twitterdj) - as well as showing up in each contributors Twitter status
Basically, when you click receive the Twitter message, they provide an URL for artists that resolve to their “FoxyTunes Planet” mashup (which pulls in YouTube, Pandora, Last.fm, Flickr and lots of other feeds). Also, when you visit either my DJ channel (or the aggregated channel), you can then listen to the songs I've recommended since they map them to YouTube videos. Voila... personalized radio that doesn't cost them anything to broadcast.
If this takes off for them it will generate a good number of page views for them without actually having to generate any content themselves. There is a growing trend of Music 2.0 services using freely available/licensed music videos to create "personalized radio stations". I'm not sure how this trend ultimately gets reconciled with the Streaming Radio Royalty Rates, but obviously more and more loopholes and workarounds pop-up everyday.