I'm working on this since months during some spare work time at my company and before knowing about turntable.fm.
Maybe some office worker here have the same niche problem as we did and find this useful. Feedback highly appreciated.Intro (telling the story behind it): http://shufflingsux.appspot.com/html/radiocracy.html
Try it: http://shufflingsux.appspot.com/html/radiocracy_new.html