Okay, I'm not going to argue that Facebook has had more than a billion Earthlings sign up for a Facebook account. And maybe the number of active users could be in the hundreds of millions. That's even with tens of millions abandoning the social network.
But for privacy-challenged Mark Zuckerberg to try to get to the next billion, it will take a lot of work. And in fact, it could be this effort that will doom Facebook down the road.
Before we go on, I want to say that the idea of a social network isn't a bad idea. Used correctly, it could be a benefit to a vast majority. Use it to promote social issues, bring like minded people together, or promote some sort of agenda (good or bad).
However, most users are doing what Facebook wants them to do: become the product which it can sell to advertisers.
In a guise to try to get more people on the Internet, empower them if you will, Facebook is looking for more drones. Not the Star Trek Borg drones but those billions plugged into the Matrix types. And perhaps there is also an element of the Borg Collective in this: individuality could be in peril as self-censorship and false attempts to maintain privacy take hold.
I suspect that if Facebook does succeed in getting it's next billion, it'll be a while but Zuckerberg will find that next billion vastly different from the first.