Weather the original intention of Facebook was to gather demographic information or not, that is what it is now, the 3rd largest community population in the world, behind India & China, at its main purpose now is to collect aggregated information on who you are, what you do, what you like, who you are friends with and where you live.
Facebook is just like the episode of the Twilight Zone when the aliens come to Earth pretending to help us out. After a while the scientists figure out that the book the aliens were following was a plan, how to serve man. In actuality they weren't trying to help us they were following a cookbook, "How to Serve man."
Additionally, as Facebook states, Facebook is free and always be free. They do not need to charge a price for admission because they are hard at work selling your information for profit.
For retailers and marketers, there is no more complete solution for laser targeting customers & potential clients than Facebook.
If you have ever created a marketing campaign on Facebook you have seen just how targeted it is. Simply, they ask who you want to target, where they live, their relationship status, what their interests are, how old they are, if they have children or not, and from there you can place your ads in front of the specific people you wish to appeal to.
So the next time Timeline is updated, or the layout changes or a stream of updates on the right or there is a any other change in the Matrix, remind yourself, this is a product you, along with 900,000,000 people statistically spend an average of 15 hours a month on. Probably almost as much time as you spend watching TV, that you don't pay a dime for. What is the cost of all of this joy & happiness, knowing that you made Facebook worth over $100B and made Mark Zuckerberg worth over $15B (at the time of this post).