Facebook

• Disallow Google etc to find your Facebook-Profile:
  Account -> Privacy -> Search -> "Public Search Results" = [ ] [1]
• If you once let Facebook check your eMail addressbook for new "friends" (=import friends) you should force Facebook to forget the addresses it found there by opening this page: [2]
• Privacy Settings -> Applications and Websites -> Instant Personalization Pilot Program -> Uncheck "Allow select partners to instantly personalize their features with my public information when I first arrive on their websites." [3]

Note: the Facenook-links above will only work if you are logged in into Facebook...