This is something people have been saying since long before facebook when myspace was the undisputed king of social networks. As early as my freshman year of highschool nearly 8 years ago teachers and administration were telling us to be careful what we put on the internets and the myspace because our prospective colleges and jobs would be looking at them.

I hate to generalize and single out a group, but of the people I know I feel like the only people who didn't understand that facebook had very little privacy were the older parents and family and such who all joined after they saw all their kids doing it.

+1 This is exactly the issue. There are many, many people out there that don't feel like something is a problem until it literally bites them in the ass. This applies on and off the Internet.