Yeah, I did not foresee that; it's actually quite critical you use Facebook.

Anything requiring the users to confirm they don't know the name of the other party slows the process quite some and removes the laissez-faire element.

This is one of the very few fair reasons to use facebook. However, I would have liked to see the explanation in the website (why only facebook?) and a stronger wording telling what you will and won't do with facebook. You're saying "We won't post on your behalf" but you don't say anything about what you will do. You might not post on my facebook, but you might be looking through my messages; that kind of thing is unfortunately the hallmark of facebook itself. Without an explanation, a facebook-only site looks very fishy. (heh)