In a nutshell.. user contributed content, original content, good SEO, and monetize on views. It pretty much takes care of itself with little effort. If you look at what stackexchange they pretty much commoditized the tech.
i think it's one of those group coupon-type industries. the potential has always been there, but nobody has fully executed on the potential.
to dan's point: i'm a big believer that some of the best ideas sprout from areas in the larger corporation that just don't get enough attention. yahoo is focused on a little of a lot, whereas quora has a lot of a little in mind.
i personally think quora is the next big thing, and to that end, i've already started including my profile in my email sig :)
