While having 300 million members is "a large number," it's just a start on the social-networking company's goal of connecting "everyone", Zuckerberg said in the company's official blog.
As the user base continues to grow, the company faces "fun and important challenges" related to making the Facebook site perform faster and more efficiently, he said, perhaps alluding to Facebook Lite, the new stripped-down version of the site that is built for speed and has been well-received.
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The company, which is privately held and doesn't offer a lot of financial details about its business, had expected to be free cash-flow positive next year, but achieved that goal in this year's second quarter instead, he said.
This means that Facebook now generates enough cash from business operations to cover the cash it spends on capital expenditures, a source familiar with the matter said. It doesn't include cash generated from things such as private investments that aren't directly related to the company's business performance, this person explained.
"This is important to us because it sets Facebook up to be a strong independent service for the long term," Zuckerberg said.