David's got this right...

Link: VentureBlog: Social Networks 3.0.

After a fair bit of excitement and energy around pure play social networks, it became clear that the building and management of a social network was not, in and of itself, a compelling consumer experience. In a nod back to the earliest instantiations of social networking, entrepreneurs have come to realize that social networks are enablers of other compelling consumer experiences. Thus, social networks are becoming an important ingredient of all sorts of consumer experiences.