I'm less interested in how people are following each other and more interested in how they are following topics and tweets themselves. People are following more key words and concepts and more ideas and acting on those rather than individuals or organizations.

It's really complex to make something simple.

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 was fascinated with jeans, because you can impress your life upon the jeans you wear. The way you sit imprints on the jeans.

You don't have to start from scratch to have a massive impact on the world.

The interesting products out on the Internet today are not building new technologies. They're combining technologies. Instagram, for instance: Photos plus geolocation plus filters. Foursquare: restaurant reviews plus check-ins plus geo.

Making something simple is very difficult.