When I signed up for facebook it suggested friends that I had no connection to outside of e-mail, and afterwards has suggested friends that again I have no connection to outside of e-mail, so my experience is in direct conflict with yours.
They do (or at least did) allow FB Connect using sites to check whether an existing e-mail address was associated with a facebook account via submitting a hashed copy (if memory serves, it's a plain md5 hash). Their developer site is down at the moment so I can't verify the exact mechanisms they (claimed) to be using to store e-mail addreses, and which e-mails they store, and what you can access through the Connect API.
* shrug * I may not have had enough friends-through-email for them to crop up. My experiences are also with an account that's been around since I started college 5 years ago, with friends who came at nearly the same time, so it could be that they added it later. Good to know for sure that they do do this, though, thanks for the reply.
They do (or at least did) allow FB Connect using sites to check whether an existing e-mail address was associated with a facebook account via submitting a hashed copy (if memory serves, it's a plain md5 hash). Their developer site is down at the moment so I can't verify the exact mechanisms they (claimed) to be using to store e-mail addreses, and which e-mails they store, and what you can access through the Connect API.