If I were starting now I would do things very differently. I didn't know anything. In Silicon Valley, you get this feeling that you have to be out here. But it's not the only place to be. If I were starting now, I would have stayed in Boston. [Silicon Valley] is a little short-term focused and that bothers me.

I think people tend to be worried about every new technology that comes along.

People wait until late in their career to give back. But why wait when there is so much to be done?

When I started Facebook from my dorm room in 2004, the idea that my roommates and I talked about all the time was a world that was more open.

Right now, with social networks and other tools on the Internet, all of these 500 million people have a way to say what they're thinking and have their voice be heard.

Advertising works most effectively when it's in line with what people are already trying to do. And people are trying to communicate in a certain way on Facebook - they share information with their friends, they learn about what their friends are doing - so there's really a whole new opportunity for a new type of advertising model within that.

When I'm introspective about the last few years I think the biggest mistake that we made, as a company, is betting too much on HTML5 as opposed to native... because it just wasn't there. And it's not that HTML5 is bad. I'm actually, on long-term, really excited about it. One of the things that's interesting is we actually have more people on a daily basis using mobile Web Facebook than we have using our iOS or Android apps combined. So mobile Web is a big thing for us.