Few social networks currently charge money for membership. In part, this may be because social networking is a relatively new service, and the value of using them has not been firmly established in customers' minds. Companies such as MySpace and Facebook sell online advertising on their site. Hence, they are seeking large memberships, and charging for membership would be counter productive.
Some believe that the deeper information that the sites have on each user will allow much better targeted advertising than any other site can currently provide. Sites are also seeking other ways to make money, such as by creating an online marketplace or by selling professional information and social connections