“The share of adult internet users who have a profile on an online social network site has more than quadrupled in the past four years — from 8% in 2005 to 35% now, according to the Pew Internet & American Life Project’s December 2008 tracking survey.”
That’s from a Pew press release. Here is more:
Most adults, like teens, are using online social networks to connect with people they already know.
See the whole report here.
As you might know, the Harnisch Foundation under the direction of Ruth Ann Harnisch gave us a substantial gift to start the Center for for Sustainable Journalism at Kennesaw State University. We are up and running. Keep abreast of what is happening at SustainableJournalism.org 
Leonard Witt is the Robert D. Fowler Distinguished Chair in Communication at Kennesaw State University and the chief blogger of PJNet. His academic interests include public and citizen journalism and how to get citizens' voices heard. He has spent most of his professional career as an award-winning journalist.