So you're trying to get a bunch of privacy concerned bitcoin users...to give you their Facebook information? Pass.
Totally respect you passing sir!
Facebook has spent a good amount of resources studying to prevent fraudulent account signups. Piggybacking that technology for the time being allows Dingb.at to better identify real people & email addresses.
What dingb.at essentially gets back from Facebook: name, email, facebook uid, friend uids. The app checks the number of friends each user has in an attempt to ensure they're real. At anytime the dingb.at app can be unlinked / removed from a user's Facebook account.