As a developer and user, I love this. For many small apps, it just doesn't make sense to ask people to create a username/password, but I still want a way of authenticating them. This move gives me a way to leverage Facebook for that without users giving up any privacy. A total win/win.
Actually at least for me, the concerns are the opposite. I do not want Facebook to know what I am doing. I do not mind you getting my name (though I would consider it rude not not accept a pseudonym of my choice).
As a developer with a production mobile app that uses Facebook for more than just sign in, I hate this. It changes a lot of the fundamental things that we use in a way that is detrimental to our user's experience.
Before, login with Facebook provided a better and more convenient user experience. Now it just seems clunky. Without the information that we get from Facebook for a user that decides to sign in with Facebook, we don't even have a user.
