A lot of our success came from George, the lead designer, and Caterina. Both of them spent a lot of time in the early days greeting individual users as they came in, encouraging them and leaving comments on their photos. There was a lot of dialogue between the people who were developing Flickr and their users to get feedback on how they wanted Flickr to develop. That interaction made the initial community very strong and then that seed was there for new people who joined to make the community experience strong for them too.
Source: Flickr founder: Creativity is human nature: http://www.cnn.com/2007/TECH/01/17/global.office.flickr/
Contributed by: ~C4Chaos