Choose something you are passionate about - or a pain point that has affected you and that you feel really needs to be changed.

Consumers are empowered by Yelp and tools like it: before, when they had a bad experience, they didn't have much recourse. They could fume, but often nothing else other than tell their friends.

In early 2008, it was confirmed that there would be an opportunity to build applications for the iPhone. We were fortunate enough to make the right call on that: to bet early, to put resources into it and have a pretty good application in the store at the moment when it opened.

On mobile, what are the core apps? It's basically messaging, mapping and review data.

A lot of what Groupon is generating is demand for something people didn't know they wanted.

One of the challenges of buying local advertising is, how do you know if it worked? How do you know if it's got value? We're moving toward an e-commerce experience for local, an Amazon-like experience for local.

About every year or two, there is a moment of truth where there's some new development in the marketplace, some new technology, some sort of existential crisis. You just have to be vigilant about looking out for those moments.