At the end of last year I wrote:

Web 2.0 is about using the Internet for what it’s good at: building web applications that enable and benefit from human social behaviour on a massive scale.

I came across this recent post by Jason Kottke which might back this up. He notes that Alexa's traffic stats put Fotolog at number 26 on the list of most popular sites, while Flickr, despite all of Yahoo's backing, is down at 39. He then postulates a reason for this:

Flickr is more editorially controlled than Fotolog. The folks who run Flickr subtly and indirectly discourage poor quality photo contributions. Yes, upload your photos, but make them good. And the community reinforces that constraint to the point where it might seem restricting to some. Fotolog doesn't celebrate excellence like that...it's more about the social aspect than the photos.

And the conclusion he draws is:

Maybe tags, APIs, and Ajax aren't the silver bullets we've been led to believe they are. Fotolog, MySpace, Orkut, YouTube, and Digg have all proven that you can build compelling experiences and huge audiences without heavy reliance on so-called Web 2.0 technologies. Whatever Web 2.0 is, I don't think its success hinges on Ajax, tags, or APIs.

Fotolog, MySpace, Orkut, YouTube, and Digg - all intensely social applications built on (with all due respect) what many Web 2.0 pundits would brand as mediocre technology.