Which brings up a related but slightly OT subject.
I am sure it is SSI top secret, but. . . Every ten years when you send in your PP for renewal, does/might the US State Department take that opportunity, before they void it and send it back for you to keep, to thumb through your pages of stamps and add them to your personal database so the computer can see if they match the airline tickets you have purchased and your customs recorded border crossings, etc.? Or see if you might have used foreign purchased air tickets or unrecorded cash travel like trains or busses to visit "countries of concern"?
[/remove tinfoil conspiracy hat]