Opting out in that manner (not existing as far as Facebook is concerned), is effectively flat-out impossible. If other people know you exist, and a HUGE amount of people are on a website, uploading all their info, you can't prevent it. It's entirely out of your control.
As to his fear that they're associating friends by email addresses uploaded, my personal experience implies that they either don't, or it factors in very lightly. A few friends who I email with pretty regularly, and are on Facebook, and uploaded their email lists (which I am most certainly on) didn't come up as possible-friends ever. It seems to be entirely friend-of-a-friend based, and as they were in an entirely separate circle of friends, they never came up. I never bothered adding them, because we already contacted each other as needed through email / IM.
The friends it did suggest to me, though, were almost universally friends of my friends, typically with several connections, but I seriously doubt they ever had my email (or many of the in-between links, if any).
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.
As to his fear that they're associating friends by email addresses uploaded, my personal experience implies that they either don't, or it factors in very lightly. A few friends who I email with pretty regularly, and are on Facebook, and uploaded their email lists (which I am most certainly on) didn't come up as possible-friends ever. It seems to be entirely friend-of-a-friend based, and as they were in an entirely separate circle of friends, they never came up. I never bothered adding them, because we already contacted each other as needed through email / IM.
The friends it did suggest to me, though, were almost universally friends of my friends, typically with several connections, but I seriously doubt they ever had my email (or many of the in-between links, if any).