Book recommendation site Goodreads says it now has more than 10 million members--making it the world’s largest site for readers and recommendations.

Although the site, which makes its money on advertising revenue, launched in January 2007, CEO and co-founder Otis Chandler says Goodreads has doubled its user base in the last 15 months. Usage jumped in the wake of the site's March 2011 acquisition of Discovereads; Goodreads integrated the smaller site's algorithmic recommendation technology six months later.

“It’s been a long time in the making,” says Chandler. “We have been growing steadily, but last year really was the breakout year.”

The Discovereads technology gave Goodreads the ability to make Netflix-like recommendations for readers--replacing an earlier manual process. Chandler says Goodreads also got a boost from integration of the Facebook Open Graph app, which allows Goodreads users to share their recommendations via Facebook.

“This is crucial for our business," says Chandler. “It used to be that authors’ primary worry was getting published. Today it's discoverability. This technology helps solve that problem.

“People want to share what they are reading and people want recommendations,” he adds.

Total funding for the company is at $2.75 million.