The Long Tail captures the observation that often demand (for a product, information or service) is characterized by a power law, i.e., a decreasing curve with a small number of highly frequently occurring events and a very large number of events that occur with a low frequency [3, 14]. In the physical world, the limited shelf-space cuts the growth of the tail. However in the digital world, with its virtually unlimited space, no barrier hinders the growth and thus enables reaching critical mass of demand even for niche-products. Web 2.0 sites often especially cater for the Long Tail, for instance by facilitating community building.