I doubt if this will surprise anyone. Facebook is a service that resides on the web. As such, all Internet rules apply to Facebook, including: If you’re worried about keeping something completely private, don’t put it online.
You can read more in an article by Emil Protalinski at http://goo.gl/LhwBjp.
I suspect that employees of many other online companies can do the same. Facebook is simply a bit more blatant than the other companies.