SpotDJ lets users record radio commentary tied to songs in iTunes. Other users can hear that commentary after listening to the same songs. After hearing an inserted DJ spot, you can rate it on a scale of 1 to 5 and other users will always hear whatever spot is rated highest by others for a particular song.
Users can set preferences as to how often they want to hear DJ spots and can chose to only hear spots from user DJs they have added to their favorites list.
From Techcrunch
