From a Kenyon & Kenyon newsletter looking at legal trends for 2013:
An important “Right of Publicity” issue for 2013 is the use by social networks of their members' names and/or likenesses in advertising. Many social networks have broad Terms of Service which purport to allow them to exploit any content that a member posts on the networks' websites. Social networks take the position that these service terms permit them to use aspects of their members’ identities in advertisements appearing within the social networks. As social networks grow and compete for advertiser dollars, they will naturally want to allow advertisers to create the most effective ads possible. Studies have shown the persuasive potential of an online connection's recommendations (due to the apparent lack of bias), and therefore many advertisers are likely to request advertising that uses the identities of a social network's users.