I have no idea how I'd give you my 'facebook address' - you'd look me up, but it might be private, or you might find the other one of me with my same name, or... I dunno. Problems.

If you send them an email with your FB page in it, a certain % will follow then, because it's a way to get some more passive updates when they want.

EDIT: 30 years ago, everyone would have given you a street mailing address, even though some possibly had faxes or may have wanted a phone call or to be paged when you had updates.