1. You give away your Facebook info.
2. Your account will become hacked, and your password and other login details will be changed.
3. The hacker, at this point, will use your account and attempt to scam your other FB friends, trying to get them to enter their information so they can be hacked.
If you want more info on this scam in particular, go here: http://facecrooks.com/Scam-Watch/warning-announcement-from-faceb00k-verification-team-all-profiles-must-be-verified-before-1st-june-2012-to-avoid-scams-and-scams-under-sopa-act-the-unverfied-accounts-will-be-terminated-facebook-s.html