DIANE SAWYER: 500 million. You are the third largest country in the world now officially. What did you do to celebrate? Did you do one, "Yes!"

MARK ZUCKERBERG: The main thing that we did to celebrate here was every employee of Facebook took a photo of themselves with a sign that they made saying 'thanks' to the people who use the service. Right, because it's really the people who make the service.

DS: Is your dream to be the 'founding father' - ha, I'm joking - to be the founding father of what, globally? Fill in the blank.

MZ: You know, the way we think about what we're doing is just that there is this incredible movement on the internet toward people being empowered to share what they want and stay connected to people. We certainly weren't the first people to do this.

DS: It's just a conversation, you're not designing the end result.

MZ: No, I mean, people make that up for themselves. That's the power of Democracy and these systems is that when you give everyone a voice and give people power, the system usually ends up in a really good place. So what we view our role as is giving people that power.

DS: Famously, Zuckerberg's little college campus networking site grew so fast he was offered a billion dollars by Yahoo! two years later and he said 'no.'

MZ: We really just believe in what we're doing. Right, it was a difficult decision.

DS: Yea, but you can believe in what you're doing and take astronomical amounts of money for it too.

MZ: Well we just felt that doing that and going down that path would not help us build Facebook out to what we thought it could be.

DS: What does it mean to you to be a billionaire right now?

MZ: Well, I'm not. I mean the company is a private company so I don't really have access to any money like that.

DS: I read once that you said you did want a jet. You wanted your own plane.

MZ: I don't think I ever said that.

DS: I know it's a private company; how much profit? How much income? How much profit.

MZ: Well we're not going to answer that. That's the advantage of being a private company.

DS: Want to give us a hint?

MZ: Nah.

DS: The business world is salivating over the possibility of a public stock offering - IPO.

MZ: When it makes sense. We're not running the company to do that; we're running the company to serve more people.

DS: But all of this has come at a stormy and legal price for Zuckerberg, from college acquaintances who say he took ideas and went off on his own. What do you think you could have done differently in those days that might have prevented the splintering and acquisitions and friendship -

MZ: You know, I started the site when I was 19; I didn't know much about business back then -

DS: But you now looking back - if you could tell that 19 year old kid something what would you tell him?

MZ: I think that the things that you learn along the way are part of what makes you who you are -

DS: Anything you would have done differently?

MZ: I mean I would have done a lot of things differently. I'd hope that instead of making the mistakes I'd made I would have made different mistakes, but I think that this has been an extremely educational experience.

DS: Some of it bruising for you inside?

MZ: Well I think all mistakes are - when you break up with a girlfriend or have a failed relationship; you learn from that and that's part of what makes you what you are.

DS: Even this week, another case; his team was in court because a man said Zuckerberg had given him a contract giving him 84% of the company.

MZ: We are quite sure that we did not sign a contract that says that they have any right to ownership over Facebook.

DS: Another rough patch for Zuckerberg - an outcry from users about Facebook and privacy.

MZ: Yea, we've made mistakes for sure.

DS: Some pretty complicated default settings - if you don't change them, you could send your private photos and postings; not just to friends, but everyone. He says they worked to change that. Do you think they're clear now? Clear, simple? I mean people keep saying 'just have an opt-in on every single thing.' What about just changing the default setting I guess is the bottom line question.

MZ: I think the right thing is to make it so certain information by default is always private.

DS: So no plans to change the default?

MZ: No, I think it's set in the way that helps people share in the way that most people want to on the site.

DS: Our back and forth lasted quite some time - you can watch it all online, but there is no question the famously camera-shy Mark Zuckerberg has created a global phenomenon that has gone from 440 employees to 1600 in just two years. Do you know all of their names?

MZ: No. I do not know a thousand people's names.

DS: What is it to be 26 and sitting astride this thing?

MZ: Um, I think it's really exciting. I mean right, a lot of the people at this company are part of the first generation of people who really grew up with computers and the internet.

DS: I'd say you're getting up there - are you worried about the 15 year olds coming and taking you here?

MZ: You know 15 year olds say the funniest things - you know I was talking to a group of high school students and the person actually told me that she thought that email was too slow, and my reaction was 'are you kidding?' email is instantaneous.

DS: So do you hate interviews?

MZ: I like how you just say that with a completely straight face.

BREAK

DS: Finally tonight a few facts about Mark Zuckerberg, the 26 year old at the center of the headlines on Facebook. His Mom is a psychiatrist, his Dad is a dentist. They started him on computers in the 6th grade. He dropped out of Harvard, but started Facebook reportedly because he was awkward getting girls. Whatever the truth of that, he has an office now like no other.

MZ: The most important thing for me is to be in walking distance to the office.

DS: And your girlfriend is in medical school?

MZ: Yea, she's a third year in medical school.

DS: So this whole idea of a lonely guy starting Facebook because he didn't have a girlfriend. Got broken up with - that's part of the creation myth?

MZ: I think people have a lot of fiction.

DS: So I have a thousand questions from people saying 'how much of his private information does he let his Mother see?'

MZ: I'm - I'm pretty open with that.

DS: She can see it all?

MZ: Yea, my Mom is my friend on Facebook and my friends can see everything.

DS: What did they say to you about all this?

MZ: You know they've always just been really supportive all along the way. When I dropped out of college um to start working on Facebook full time out here I later talked to my Mom about it and she told me that she knew I was going to drop out of college. [laughs]

DS: That college was Harvard and as we said there were bruising arguments with students there who said they too were once part of the social networking design. Once of those closest to Zuckerberg - once his roommate - reportedly behind a big new movie. Have you seen the trailer for the movie, The Social Network?

MZ: Um, you know someone showed me part of it.

DS: Are you going to go see the movie?

MZ: I don't think so.

DS: Would you like someone else to play you? Are you happy with your -

MZ: I don't know, I've never met him. He seems like a nice guy. Actually his cousin works here.

DS: What?

MZ: Yea, his cousin is a designer here - we have meetings all the time. We're working on designing a program together. Yea, it's a small world.