I think it's worth pointing out that on Twitter, there is only one privacy setting, when you set up an account, and you have complete access to who sees your tweets. Unless I missed a major news story about this, I don't think Twitter has yet violated anyone's trust there.
Facebook, on the other hand, by either incompetence or some skewed sense of openness, at some point has made a choice that it wants to put all your information out there while giving you the illusion that you have some control over it.
The point is that privacy isn't impossible. It's simple. You have an element in a database that is flagged as important to someone, so you make sure that before you ever pull that element out and put it on the web, the proper controls are in place. It is just a choice a company makes of how high of a priority to make something, and Facebook has demonstrated that privacy means more to them as a PR issue than a real concern about user data.
Facebook, on the other hand, by either incompetence or some skewed sense of openness, at some point has made a choice that it wants to put all your information out there while giving you the illusion that you have some control over it.
The point is that privacy isn't impossible. It's simple. You have an element in a database that is flagged as important to someone, so you make sure that before you ever pull that element out and put it on the web, the proper controls are in place. It is just a choice a company makes of how high of a priority to make something, and Facebook has demonstrated that privacy means more to them as a PR issue than a real concern about user data.