Quora does not do it very well – they are not exactly taking over the world with growth. Q&A is not a panacea; it does not fit all topics, in fact it only really fits a minority of them.
I feel Quora doesn’t even understand the actual strengths of the Q&A format, as we did at Stack Overflow.
Quora is a fantastic resource. But it will never have growth or usage rates comparable to Facebook, Twitter, Instagram et al, because it’s sheer human nature to prefer conversation to answers; and it will never be quite as absorbing as Wikipedia, because other people’s questions are never as interesting as our own. It’s a fascinating mélange of encyclopedia and social network, but alas, I fear that in terms of widespread success and adoption, it combines the worst, not the best, of those two worlds.