It's been reported that Facebook will reach 500 million users this week. That’s a 5 with eight zeros. Or in people terms it’s the combined population of the United States, Japan, and Germany—or half the population of India.

However you think about it, it’s a lot of people looking to connect. In the last year the number of Facebook users has doubled in size. In just 6 years it’s become the biggest information network on the Internet— or anyplace else, for that matter. And Facebook effects go well beyond just sharing photos or saying ‘hi.’ For many it has become the site of first resort: 70% of users outside the U.S. and 25% of all users check in and update their pages via cell phones. And all this has begun to test the limits of personal privacy.

When you’ve got a half-billion users distributing personal news, views, and information of both real and sentimental value, you have to also be able to manage the masses of enlightened – and humdrum – personal information shared by the masses with the masses. Last year the company’s change in privacy policy sparked complaints by users on comment boards and privacy groups to regulators. This year there’s also been a lot of uproar online about Facebook's alleged lack of concern for the privacy of its users' personal information, and complaints that the 45,000-word privacy policy is far too complicated for an ordinary user to decode.

This growth and privacy uproar has attracted the attention of Federal regulators and lawmakers who are looking to protect the privacy of consumers, because the number of users isn’t the only thing growing. Third-parties such as advertising networks, with access to all this information, make it important that consumers understand what they “own,” what is actually being shared, and which privacy rules apply.

Nearly 4 decades ago, Earl Warren noted that the advances in electronic communications constituted a real danger to individual privacy. That said, according to our Customer Loyalty Engagement Index (and varying, of course, depending upon the category you’re talking about), aspects related to privacy have only increased only very slightly over the past 5 years. Times have changed and Americans are apparently willing to trade a degree of privacy in exchange for on-going social networking. But for vacation photos?

As frustrated execs and users throw up their hands and ask, “what do people expect?” Facebook's growth will have more to do with how well it listens and changes according to users expectations as to what’s private and what isn’t. As big as Facebook is, it might want to tread carefully and not only help users “friend” someone, but be one.