Facebook in particular had some major privacy issues. I think they have improved on them greatly.
My impression is that they've gotten just worse and worse. With Facebook you pretty much have to assume that anything you post will become 100% public at some point or another, since they keep changing what the privacy settings mean and how things work with little warning and unless you keep an eye on your privacy settings, suddenly you'll find that something has changed visibility of your stuff again.
I have a Facebook account, but nearly every privacy setting is set to the max and I only ever post things I'd be equally happy to put on my blog for the entire world to see.
