From an Inc.com article about the birth of Flickr: (via UIE Brain Sparks)
George Oates and Caterina Fake 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.
Social in both senses. I’m not going to use the word ‘viral’, because I hate it, but it’s clear that Oates and Fake’s hard work paid off. But it outlines the need for community building on the web; users as evangelists and promoters, the audience handing out their own flyers.