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

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

Yelp is in a very nice spot: local data, and especially review data, is one of the killer apps on mobile phones.

You have to be very nimble and very open minded. Your success is going to be very dependent on how your adapt.

The biggest thing is to create a product that consumers find useful. As more and more people like something, it becomes harder and harder to have a conspiracy theory about it.

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.

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.