Seems like a good place to ask this: are those 'sign in with Facebook' buttons trust-worthy? I've only clicked one of them, and that was a 'sign-up' button fo

Seems like a good place to ask this: are those 'sign in with Facebook' buttons trust-worthy? I've only clicked one of them, and that was a 'sign-up' button for an event i will be physically attending everytime i see one, I worry that a) it's going to broadcast to my entire friendlist that i signed up for this service b) it's not a REAL facebook button, but something to phish my account c) this site will know my Facebook login d) some other party will intercept the login... tell me it's completely safe?