The privacy thing I've never understood is why you can limit your profile visibility for a "friend" who is really an acquaintance, but if on a stupid whim you do decide to take one of those stupid quizzes, the application's owners get to see your entire profile, including (so I'm told) some data that you needed to sign up but isn't actually on your profile page. That's why your spam levels will go up even if your e-mail address isn't public.