What about "Yes, but I don't use it.". Some sites force you to use a Facebook login, so I created an account but it has nothing on it but my name (no pics, etc.).
I'm the same so I put "Yes but I want to leave" because essentially you were forced into an account in order to use the login (meaning you wouldn't be on if you'd had a choice and hence you want to leave)
It would be interesting to see that numbers that equate with this, or with people who wish to have a FB business page so sign up with an empty personal page.
I only have a link to my twitter profile in my facebook profile