Recently, almost everything seems to have become "2.0", be it music, gadgets, health, entertainment, business, Silicon Valley, countries such as India, the family, and, most notably, the Web. 10GB of "user-generated content" is created in the World-Wide Web daily (see Ramakrishnan and Tomkins, 2007), that is, more than five times the amount of content created by professional Web editors. Web 2.0 has rapidly become a label that everybody using the Internet and doing business through it seems to be able to relate to; what it primarily stands for is the transition of the Web from a medium where people just read information to a medium where people both read and write; in other words, the Web meanwhile heavily benefits from user contributions a...