And the worst of all worlds for the user. When I use Facebook logins for a site, it's because I don't know if there's value in the site so I want signup and evaluation to be as quick and painless as possible. I don't want to have to go through other steps, I want a one-click registration and login.
A pet peeve of mine is when I click on the login with facebook button and the site still makes me fill out my name, username, email address, and set a password. So what's the point of logging in with facebook?