People who count you as a friend have chosen to ask facebook to send you and email on their behalf so they can get together with you on facebook. You guys react by assuming its fraud or spam, and grumble about it on hear.

Facebook which is a far more friendly place than mudcat, perhaps too friendly for you maybe. Facebook beats forums hands down for encouraging friendly and positive behaviour, its not all friendly but it is so refreshing after the nasty evil world of forums. If you don't want to join then wouldn't an email note to the person who feels you are friend thanking them for the invitation and declining it be the best option.