In one rather striking survey Marche cites, the mean size of networks of personal confidants in the U.S. was shown to have "decreased from 2.94 people in 1985 to 2.08 in 2004." In 1985, he adds, "10 percent of Americans said they had no one with whom to discuss important matters, and 15 percent said they had only one such good friend. By 2004, 25 percent had nobody to talk to, and 20 percent had only one confidant."
You'll find Marche's article here. Meanwhile, Sherry Turkle, MIT psychology professor and author of Alone Together: Why We Expect More from Technology and Less from Each Other, has a thoughtful, entirely related op ed on this topic in today's New York Times: "The Flight from Conversation."