Silicon Valley's most talked-about new Web company, Quora, offers a novel spin on an old concept: it takes a standard Q&A site and adds Twitter-like social networking to the mix. The site has grown rapidly in recent weeks, in part because of the quality of its content and community—but now its newfound popularity may jeopardize the content that made the site a success in the first place.

Quora was founded by two Facebook alumni: Adam D'Angelo, previously the social network's chief technology officer, and Charlie Cheever, the engineer and manager responsible for creating Facebook Connect and the Facebook Platform.

Their new site launched in an invitation-only beta in January 2010. Quora's easy-to-use interface, as well as the founders' impressive connections, rapidly attracted an elite group of early users, many from Silicon Valley's most innovative companies. That meant Quora users could read the opinions of high-profile people from within the tech world, including former AOL chief Steven Case explaining the dot-com bubble, Facebook cofounder Dustin Moskovitz's opinion of The Social Network, or well-sourced gossip on Google's in-development social tools.

Quora has social- networking features similar to those of the microblogging service Twitter. Users can "follow" one another and receive notifications when people they know submit questions or answers; they can also follow certain topics or questions to keep track of new content.

Cody Brown, founder of Kommons, a Q&A site that allows people to publicly pose questions to Twitter users, says Quora's design and features create a more "structured" space for sharing thoughts than most blogging or social-networking sites. That design encourages contributions from people who might steer clear of social websites, he says: "It's not like a conventional blog or Twitter, where you are looking at a blank space and have to come up with something. You get a more specific prompt to contribute, and so it feels less narcissistic."

This approach generated the insider content that led to a recent surge in users and media attention. Yet Quora's success could endanger the very thing that caused that success, says Eileen Burbidge, a London-based investor in startups who previously served as product manager for Yahoo Answers.

"Quality of content and community is diametrically opposed to mass market success," says Burbidge. "Having worked on Answers, I can tell that the level of quality is going to drop from the very high level it is at now as more people sign up."