In the last few years, social networking sites and the uses they are generating have become a rapidly expanding star in the Internet galaxy. Among these networks, those that end users can access free of charge do not yet have a stable economic model, despite their wide audiences (Facebook, for example). The challenge now facing these networks is how to turn their popular success into actual cash; in other words, how to press their capacities for targeting and filtering web users, and the communities they form, into the service of solvent advertisers. As shown by the aka’aki example, a geolocated mobile online network, the path is a narrow one and there is no guarantee of success. Increasing suspiciousness among Internet users as regards the transformation of private information into a marketable commodity is the main limitation to the business model now emerging.