The music label, Amie Street, is experimenting with a new model for pricing digital media. Initially, downloads will be free, then increasing as they songs become popular. I have to imagine that this is enabled by a much deeper acceptance of the underlying technology. Online distribution certainly represents an opportunity to capture and analyze much more accurate and detailed data about who is buying what and hence this idea of popularity driven pricing actually makes good technical as well as common sense.
Regardless, kudos to Amie Street for just being willing to experiment in the first place.