This thrilled Zuckerberg, whose primary measure of the service’s success was how often users returned.

Revenues were, according to well-informed sources, more than $550 million for 2009—up from less than $300 million in 2008. That represents a stunning growth rate of almost 100 percent. The same sources say that the company could exceed $1 billion in revenue in 2010.

But like the best empire builders, he was both very determined and very skeptical. It’s like [former Intel CEO] Andy Grove says, ‘only the paranoid survive.

In Friendster's wake, a throng of social networking sites blossomed in San Francisco attempting to duplicate its appeal. Each tackled the idea of connecting people in a slightly different way. One was Tickle, a service which, on observing Friendster’s broad-based appeal, altered its own service, which had previously been based on self-administered quizzes and tests. Two of the other new social sites—LinkedIn and Tribe.net—were founded by friends of Abrams.

By early 2004 Tickle had become the second-largest social network after Friendster, with two million members actively connected to others and exchanging messages.

If you cannot measure it, it means it doesn't exist.