What they do: run one of the most popular sites on the Web, a free online photo-sharing service

"George Oates [a Flickr employee] and I would spend 24 hours, seven days a week, greeting every single person who came to the site. We introduced them to people, we chatted with them. This is a social product. People are putting things they love -- photographs of their whole lives -- into it. All of these people are your potential evangelists. You need to show those people love."

Read more about Stewart Butterfield and Caterina Fake