In many ways, Quora feels like a combination of Yahoo Answers, , and Twitter. On tech-related topics, it can also feel a bit like perusing the (often expert) comments on a site like Slashdot.
There are clearly many competing questions-and-answers sites out there, including not just Yahoo Answers but also Mahalo Answers, , and others. So far, Quora seems to be distinguished most by its quality focus, its stricter guidelines, and its emphasis on real identities and personal networking--not to mention the early participation of several high-profile users including .
What remains to be seen, of course, is how well the company can preserve these distinctions now that the site has begun to really grow.
In the meantime, I don't think businesses can afford to ignore it. Just as I think Stephen Fry's should be monitored by brands--particularly for the conversations that take place on top of their own company Web pages--so every brand should watch Quora for any brand or company-related discussions.