A check of
https://developers.facebook.com/status/dashboard/
returns an error and I'm unable to login with facebook to some of my mobile apps.
EDIT: Commenters are reporting that this appears to only impact users that are hitting the US data center[1], and that it may only impact users through specific ISPs
1.https://news.ycombinator.com/item?id=18434457
EDIT: Appears to be back up