Source: The Raw Story
BEWARE: Your address book has probably been updated by Facebook if you accepted the default settings when you installed the Facebook App on your Android or iOS devices. I am pretty sure that my Android phone retained all of the e-mail addresses I have entered myself, but Facebook has added new addresses to my address book and REPLACED all of the e-mail addresses that were previously added by the Facebook App. IMO, this poses a significant security risk and an even bigger inconvenience, because you could easily address your e-mail messages could easily get delivered through Facebook instead of directly to the recipient's preferred e-mail INBOX. This will be particularly problematic for people who "friend" co-workers and colleagues, because work related e-mails could be delivered to Facebook instead of the recipient's corporate mailbox.