...opening up your address book to Facebook voluntarily exposes you to not only those to whom you choose to be exposed, but to those from whom you'd prefer to be hidden.
I suppose that's true for those who leave Facebook's privacy controls configured to the wide-open settings Facebook would prefer (Facebook's goal is for all seven billion of us to have seven billion friends each), but for those who choose the most restrictive settings, the resulting "people you may know" suggestions Facebook makes to folks found in your address book don't allow those folks to know much more about you than that you exist—which, presumably, they already know, else why would they be in your address book?
