Gizmodo reports that Siemens demonstrated an application called Runster that varies the tempo of music played on a Bluetooth-enabled mobile phone based on how quickly the user moves. The idea is to allow the user to listen to songs that are appropriate to the intensity of his or her exercise. The application was demonstrated on a prototype Siemens SX2 mobile phone at the CeBIT trade show in Hannover, Germany.
I've created playlists for my wife's iPod to correspond with running and cycling workouts that I do in the hockey offseason. These playlists have different tempos that I think are appropriate for the pace of my exercise. I think I will be using applications like Runster in the future during training and I hope that a feature like this comes out for the iPod platform some day.