john doerrMore venture capitalists have an embarrassing, “I can’t believe we didn’t invest in that company” moment. For Kleiner Perkins Caufield & Byers’ John Doerr (whose past investments include Amazon.com and Google), it sounds like one of those moments involved turning down a chance to invest in Twitter.

When Twitter’s founders approached Kleiner, Doerr said it was very early, the company didn’t have any users, it didn’t have any traction, “It wasn’t Twitter.” Doerr said that Twitter has now become an “incredibly powerful information network” but not a social network. Summing up the decision, he said: “We were wrong.”

For the past few years, Kleiner appeared to have backed away from non-cleantech investments in general, and social networking in particular — in part, presumably, because Kleiner had already invested in Friendster. (The firm is coming back with the $250 million sFund, building on the success of its social gaming investment in Zynga.)

Twitter investor Fred Wilson of Union Square Venture Partners was on-stage with Doerr at the Web 2.0 Summit. While the pair had been arguing pretty passionately about companies like Apple and Google, he stepped in to defend Doerr on this count. Turning down Twitter may have been a mistake, but beyond specific investments, Wilson said Doerr is still the “Michael Jordan of venture capital.”

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