It was 2004, and we were in a meeting at Google debating if Picasaweb would have comments in the first version. (There was actually a contingent saying that maybe this wasn't needed.)
And I remember this moment like yesterday. Lorna, our PM (who I married two year later, so I'm not biased at all) piped up to say, "You know, Flickr gives people who look at your pictures something fun to do. It's all about the audience." Blink.
This view won several years later, and it's one of the biggest network effects online today. You don't make photo sharing sites that make it easy to share photos--it doesn't matter. You make photo sharing sites that give you an audience for sharing. That's Facebook, and it's the reason it is so very hard to compete with Facebook right now. Best audience, and the rest doesn't matter.
I keep telling people if Facebook made it nightmarishly hard to post a photo, 10x harder than today, it actually wouldn't matter much. People would figure out how and keep doing it, because the audience is there, and they like being there. They look at me like I'm insane for a few seconds, and then it usually clicks.
Moral of the story: when you "focus on the user", it's important to know who the user actually is.