Facebook still has plenty of room to grow, particularly in developing countries where people are only starting to get Internet access. As it is, about 80 percent of its users are outside U.S. and Canada.
But if Facebook is to live up to its pre-IPO hype and reward the investors who are clamoring for its stock this week, it needs to convince some of the resisters to join. Two out of every five American adults have not joined Facebook, according to a recent Associated Press-CNBC poll. Among those who are not on Facebook, a third cited a lack of interest or need.
If all those people continue to shun Facebook, the social network could become akin to a postal system that only delivers mail to houses on one side of the street. The system isn't as useful, and people aren't apt to spend as much time with it. That means fewer opportunities for Facebook to sell ads.
Lee Rainie, director of the Pew Internet & American Life Project, says that new communications channels — from the telephone to radio, TV and personal computers — often breed a cadre of holdouts in their early days.
"It's disorienting because people have different relationships with others depending on the media they use," Rainie says. "But we've been through this before. As each new communications media comes to prominence, there is a period of adoption."
Len Kleinrock, 77, says Facebook is fine for his grandchildren, but it's not for him.