In what seems to be an attempt to push its products on those who don't take the extra steps to fix them, facebook recently changed everyone's listed e-mail address to @facebook.com without asking or informing anyone.
Even better, it would appear that the integration between iOS6 and facebook on the iphone means that multiple beta testers have lost all their e-mail contacts as facebook updated their phone contacts with @facebook.com e-mails. Again without asking or informing the user.
Facebook's Email Overhaul Is Seizing Smartphone Contact Lists, Reports Say | Gadget Lab | Wired.com
They are claiming it's a bug. Facebook integration doesn't sound so cool if it's going to accidentally take over and modify your phone or other devices. I hope there's a way to turn this integration off in iOS6.