“From time to time, most people discuss important matters with other people. Looking back over the last six months--who are the people with whom you discussed matters important to you?”
The General Social Survey, a project of the University of Chicago’s National Opinion Research Center, asked that question in 1985 and again in 2004. The results were surprising.
(FYI, this isn’t just any poll. The GSS is the gold standard of impartial public opinion research, conducted face-to-face with a random sample of 3,000 Americans every other year. It's been a model of caution and care in tracking public opinion on general subjects since 1972, and on some subjects well before that. More.)
Twenty years ago the average person had a “network” of three people with whom he or she could talk over important matters. Now it’s down to two, and those two are more likely than before to be family members, rather than neighbors or coworkers. In 1985 about 10 percent said they had nobody to talk to; now it’s 25 percent.
Miller McPherson of the University of Arizona and two other sociologists report the findings in the American Sociological Review. Money quote:
“In his groundbreaking  study of social networks, To Dwell Among Friends, Claude Fischer labeled those who had only one or no discussion ties with whom to discuss personal matters as having marginal or inadequate counseling support. By those criteria, we have gone from a quarter of the American population being isolated from counseling support to almost half of the population falling into that category.”
No one study is conclusive but this is a solid piece of evidence that’s pretty hard to spin as good news. Unlike many GSS questions, this one hasn’t been asked in every survey, so there aren’t as many data points as one would like. And perhaps most people define “important” differently now than before, though I know of no evidence for this.