If you're not on Facebook, here's how it works: you set up a profile page with details about yourself and then decide who gets to see it. Friends use their pages to share personal news, exchange photos, team up on political causes, or just play long-distance Scrabble. It can be a useful tool or an addictive waste of time. Either way, Facebook is having a dramatic impact on the World Wide Web and it's estimated to be worth $15 billion.
As Lesley Stahl reports, sitting atop this growing company and directing an Internet revolution is a young, geeky computer programmer who created the site only four years ago.
The face of Facebook is Mark Zuckerberg, the mogul who's guiding its extraordinary growth. What everyone wants to know is: Is he old enough to be running a company some people say is the biggest thing since Google?
"I'm 23 right now," Zuckerberg tells Stahl when asked how old he is.
"And you're running this huge company," Stahl remarks.
"It's not that big," Zuckerberg says.
During her visit to Facebook's headquarters, Zuckerberg helped Stahl set up her own Facebook page, with a profile of her likes and dislikes. They added her friends and family, and within a few minutes, she got a friend request.
"Here's a guy I haven't talked to in two years and I'm so thrilled to hear from him," Stahl remarks.
This is why so many find the site addictive. In a world with no cell phone or e-mail directories, Facebook has become a way to find lost friends.
"It used to be the case, like you'd switch jobs. And then maybe you wouldn't keep in touch with all the people that you knew from that old job. Just 'cause it was too hard," Zuckerberg explains. "But one of the things that Facebook does is it makes it really easy to just stay in touch with all these people."
Of course, if someone tries to "friend" you, you can ignore them. And privacy settings allow you to deny access to your page say, to your boss or your parents.
Facebook's headquarters in downtown Palo Alto look like a dorm room; the 400 employees, who get free food and laundry, show up late, stay late, and party really late.
Zuckerberg, who's made the cover of Newsweek and is reportedly worth $3 billion, sits at a desk like the other software engineers, writing computer code.
"Have you changed your lifestyle? You don't look like you're buyin' really expensive clothes," Stahl asks Zuckerberg, who showed up to the interview in a sweatshirt and sandals.
"No, I'm not buying really expensive clothes," Zuckerberg replies, laughing.
"Are you buying things that you would be…," Stahl asks.
"Yeah. No, I have a little, like one bedroom apartment with a mattress on the floor. That's where I live," Zuckerberg says.
Kara Swisher, who used to write about Silicon Valley for The Wall Street Journal and now has a blog, All Things Digital, has called him "The Toddler CEO."
"What do you think it's done to him, as a person, to be 23 years old…," Stahl asks.
"Well, I think it's hard. I think when all of a sudden you're the smartest person in the world, and you're the meal ticket for everybody, and this is the big hit. This is the new Google at this point," Swisher says. "And so Mark is under a lot of pressure, because everybody wants something from him."
Like the founders of Google, Larry Page and Sergey Brin, Mark Zuckerberg is looked up to in Silicon Valley as a visionary.
"You seem to be replacing Larry and Sergey as the people out here who everyone's talking about," Stahl remarks. Zuckerberg doesn't reply, only stares at her at length.
"You're just staring at me," she adds.
"Is that a question?" Zuckerberg asks.
We were warned that he can be awkward and reluctant to talk about himself, so we turned for help to his Facebook page, which says he's a Harvard alum.
"You're not a Harvard alum," Stahl remarks, looking at his own list of networks.
"That's true. We don't have a setting for dropout," Zuckerberg explains.