Up to a point. However, everything you do on FB is monitored. And a lot if it is publicly visible. So just because you're not sharing your personal info that much doesn't mean that a friend can't - or won't. Many times it happens innocently or carelessly, but also sometimes when a spat breaks out. I've seen a lot of very personal info flung around when the fur starts flying in my sister's FB circle.
First rule of the Internet - it was originally intended as a network designed to survive a nuclear attack. So once something is out there, it's out there forever. You can delete data, put so-called privacy locks on it, or try to hide it. But most times anything you do is recoverable. And when it's not, there's always traces left behind. This is not paranoia by the way. This is the natural result of good network design. The only totally secure and private network is the one that's never switched on.
All true, and, as I remind my friends all the time, when a service is free on the internet, it means you are the product. Also: Never post anything that you don't mind the world knowing.