[Jessica Helfand:] The idea of social networking has always made me uneasy. To begin with, I’m not terribly social, and I don’t exactly thrill to the idea of networking, either at bars or across an ethernet. I was never a big fan of collaborative filtering — the idea that just because I bought a cookbook on Amazon, I was instantly being targeted for every ergonomically correct onion slicer on the planet — and my opinion of user testing is only marginally cheerier than my view of market research. Basically, I cling to the notion of resistance, particularly when faced with the opposite: joining.

But Flickr has changed all that.