The New York Times writes about the social networking sites:
These sites and dozens of smaller ones have something those marketers want: the attention of tens of millions of young people who increasingly avoid television commercials. So companies from Procter & Gamble to J. P. Morgan Chase, like so many lonely teenagers, are tricking out their online profiles and trying to make friends on the Web.
The sites are trying to move beyond banner ads and develop ways to integrate marketers into the fabric of their online communities. For example, marketers encourage the sites users to become friends with characters from their ads, and are experimenting with more elaborate campaigns that take advantage of the word-of-mouth effects of networking sites.