The email you use for facebook do you use for several other thing? With ecommerce your identity is no so safe, with facebook's email account search anyone can find out who you are and with a phone book they can find your place of living as well. Should facebook change this it is invasion of privacy I think !
Change your password at once after you use the friend finder function.. That will lower the cost of being leaked out if you afraid.. =)
Don't put all of your personal data on facebook, I've just removed my SSN and PayPal login information from my profile, just in case.