Sure Facebook could serve contextual ads on other sites/service based on what they know about their users, except it would violate their privacy policy.<p>"We do not share any of your information with advertisers (unless, of course, you give us permission)."<p>Correct me if I'm wrong, but it would be technically possible for a page to read and report back to the originating server what ad appeared on a page (integrated with js or iframe, etc.). This would violate that clause of the privacy policy.