Facebook has reached an almost unimaginable milestone: 1 billion people are active users. It is hard to get your head around that number, which represents one-seventh of the world’s population (and not every one of us even has Internet access). It’s almost half the total number of people estimated to be on the Web at the beginning of this year.

Even CEO Mark Zuckerberg can’t quite seem to comprehend it: “It’s really humbling to get a billion people to do anything.”

But despite gangbuster growth, Facebook is based on a tricky business model: The more they use members’ shared information to target them for advertisers and marketers, the less members are likely to go along, and the more they’ll realize the bargain they’ve struck. Just as Facebook effectively redefined “Friend,” it is pushing the boundaries of the public-private divide.

So it’s a fine line they have to walk, promising granular, voluminous, robust member data that has real value in the marketplace, while reassuring members there’s nothing to worry about.

Facebook does the latter primarily by not drawing attention to the issue at all. It has over the years changed things in ways that consistently favor increased sharing, putting the onus on members to opt out. Tech writers scream bloody murder, and yet (shockingly!) membership still rises.