It's a matter of invitations versus context. Twitter is really good at providing context, like, I''m having coffee at Third Rail Coffee.' Foursquare is about invitations to places. In this respect Foursquare has started to replace Yelp for me.

I spend 90% of my time with people who don't report to me, which also allows for serendipity, since I'm walking around the office all the time. You don't have to schedule serendipity. It just happens.

Making something simple is very difficult.

The idea of Twitter started with me working in dispatch since I was 15 years old, where taxi cabs or firetrucks would broadcast where they were and what they were doing.

A number of people in the United States, almost everyone, is using plastic cards to pay for things, but it's extremely difficult to accept these cards. So let's make it's easy and take more and more of the friction out as we can.

I am someone who tweets about what I have for breakfast, what I have for lunch, what I have for dinner, and for 99.99999 percent of the world, it's useless. It's meaningless. But for my mother, she loves it.

There's an entire universe in every single tweet, and it all really depends on the content as far as how it's going to spread.