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.

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.

IM is interesting because you look at your buddy list and, at a glance, see what your friends are listening to, what they're working on, what they're doing. The problem was that you were bound to the computer keyboard.

Twitter has been my life's work in many senses. It started with a fascination with cities and how they work, and what's going on in them right now.

I think Twitter is the future of communications and Square will be the payment network.

I love cities, and I love city governments in particular. But in politics it would have taken me 8 years from implementing a policy before I would get to see the feedback. With programming I could model the same policies and see the impact immediately. Technology is a far more efficient way to test.