Amazon recently dumped an undisclosed amount of cash into AmieStreet.com, a start-up digital music store that throws in an element of social networking: track prices rise with their popularity. A song’s price starts at nada, but as more people download it, the price tag balloons until it hits a 98 cent ceiling. The cool twist in the model is that the more popular a song gets after you recommend it, the more store credit you receive for being ahead of the crowd.
