There's been a well justified storm about Facebook's recent privacy changes. The EFF has a nice post outlining the changes in privacy policies at Facebook which inspired this popular graphic showing those changes.
But the deeper question is why Facebook wants to do this. The answer, of course, is money, but in particular it's because the market is assigning a value to revealed data. This force seems to push Facebook, and services like it, into wanting to remove privacy from their users in a steadily rising trend. Social network services often will begin with decent privacy protections, both to avoid scaring users (when gaining users is the only goal) and because they have little motivation to do otherwise. The old world of PC applications tended to have strong privacy protection (by comparison) because data stayed on your own machine. Software that exported it got called "spyware" and tools were created to rout it out.
Facebook began as a social tool for students. It even promoted that those not at a school could not see in, could not even join. When this changed (for reasons I will outline below) older members were shocked at the idea their parents and other adults would be on the system. But Facebook decided, correctly, that excluding them was not the path to being #1.