I read this recently and its worth a look if you are in anything related to marketing. The author discusses why certain products catch on and others don't. One of the best things I've gleaned from this is the use of association when marketing a product. People tend to be more drawn to a product when its associated with something else they like. One example was how the song "Friday" partially became a hit merely because people like Fridays and they happen every week. The songs popularity on the chart would increases on guess what day.....yep, Friday. It had a built-in selling point and Fridays happen every week so even better.