I wonder if we'll ever see the me-brand music experience, where shoppers carrying their own music players (iPods, cell phones, etc., which they're carrying to begin with) can approach a DJ booth and program the music for a few minutes. Stores could also take a photo of the person whose music is playing and flash that up on screens to go with the music. If the song has a video they could play that. This would work especially well for a store selling music so that peers are introducing their peers to their music that they can then buy. The store could create little mini-stars of the DJs, invite some of them back, have a top DJs list. Really, steal a bunch of ideas from web behaviour that would work in retail situations.
I know there are licensing headaches for public performance, but seriously, if you want to do it, those can be overcome.