Business Models for Social Networking Sites

As blogged about in this post, Hitwise, stated in June that 'MySpace and Facebook comprised almost 90% of the US visits to social networks'. This led the author to make the interesting point maybe this is the case not only because social networks are relatively new, but maybe because this genre of sites are still learning how to generate revenue. As the author states, 'I blame it on not thinking of a better way to monetize social networks in general.' He goes on to mention that in his opinion LinkedIn is on the right path, especially since their average user age is 40, and they have a higher purchasing power. Since the age is younger for both MySpace and Facebook, and people are still unsure how to leverage them from a marketing standpoint, the author argues that 'we're stuck with the traffic=advertising=revenue business model'
What are your thoughts on this? What do you think is the next step in the evolution of the business model for social networking sites?