Log in with Facebook
A few years ago I worked on an application that used OAuth. The idea is that instead of doing our own authentication, we delegate it to a trustworthy organisation that maintains a huge database of credentials. It's nice because users don't have to remember lots of usernames and passwords (which possibly also makes it nice for impersonators).
One of the main authentication suppliers was... Facebook. And the ubiquitous "Log in with Facebook" on web applications suggests that Facebook's involvement in authentication hasn't diminished.
In the light of this story that looks about as sensible as letting next door's goldfish take the controls of your plane.