Well StackExchange, but moreover beating out Wikipedia and Google seems to be more in line with their long game.
(e.g. "I ended up going to Quora, because I was even more passionate about the vision and the role. I had a chance to help build what could become the platform for all human knowledge, which I thought could be a revolution of the same magnitude as Google" http://www.quora.com/Instagram/Did-anyone-decline-an-offer-t...)
I don't see how they can center that vision around a question/answer format. To me it seems limited.
On a separate note, and given a recent HN discussion about some of the constraints Stack Exchange puts on free flow of discussion, I see an angle Quora can explore.
discussion is only tolerated on Stack Exchange insofar as it allows us to get better questions, and better answers to questions. Just that amount, and no more.
(note: I do not disagree that the Q&A format may not be appropriate or even correct for all topics. Particularly and perhaps most of all those with no remotely verifiably "correct" answer possible.)
Quora's Q&A format is a lot more permissive than the SE one though. You're allowed to have questions that don't have correct answers, and are asking much more general questions - discussion is more accepted.
Surveys and polls are the only question-types banned on Quora that I can recall.
