In Web 2.0, data is often as important as function. Take del.icio.us as an example: its functionality is voluntarily limited to the basic function of bookmarking with tags, however, the value of del.icio.us emerges from the massive amount of annotated resources. Thus Web 2.0 services employ different measures for increasing user contributions and participations, for instance by building trust (e.g., offering users to leave with an export of their data), by explicit licenses (often open licenses such as Creative Commons), and paradoxically, by making content accessible through RSS syndication and APIs. Behind the user-provided data of Web 2.0 lies the Semantic Web [10] with its vision to make the data currently hidden in databases available for usage by machines.