Originally Posted by ESpen36

OT: Makes me wonder how it works if you fly to Canada or Mexico and then drive back over the border (where the agent usually just glances at you and waves you through, without swiping your passport into the system). How would the CBP computer system know you had returned Stateside? Could foul things up the next time you try to leave the country by air and and the airline swipes your passport for APIS purposes prior to boarding pass issuance.

(Or are all U.S. land border stations swiping individual passports/WHTI-complaint documents for each and every traveler nowadays?)