Careful now: Using Facebook login means Facebook can lock your users out at any time.

SVT reports about yet another case of someone who got their facebook account deleted without warning. This time it's Roman Pixell. His "crime"? Like any other parent he snaps pictures of the offspring when they are in the cutest state... ie: sleeping. He posted the above image of his then 5 year old daughter fast asleep on a trendy 'nail mat', and she's not wearing a shirt in the photograph, heaven forbid!

Leaving aside the morality issues about letting kids sleep shirtless, photographing offspring when they're half-naked and/or sharing said photos with friends and family inside the walled garden (and to some the seemingly safe-haven) called facebook, Roman reveals that the deletion of his account had far reaching consequences, that we who design sites with easy-logins need to be acutely aware of. The deletion of his facebook account meant he could no longer log in to the 30-odd internet services out there he used his facebook login on.

"All of a sudden shut down my account and then I was also banned from all other services on the web where I use Facebook to login."
"You feel terribly powerless", said Roman." It was not until my Facebook login disappeared that I realized that my login to the 30 or so other services on the Internet were locked as well. And there's no way to get in touch with Facebook other than that ignored web-form."

For the "too long, didn't read" crowd, in short: If you use Facebook login as an alternative on your site, Facebook's arbitrary whims of what is against their TOS is now your problem as well.

There is no way for you to contact the user directly, or the user to contact you as no emails are registered with the facebook login. I'd steer clear of using that if I were you.