A friend of mine was heading down to the states camping this summer. He goes ever year. Well this time it was late at night and the guard had nothing to do, and he ran a check. Turned up an old shoplifting charge from when he was 18. They turned him back and now the charge is somehow more 'active' because it's been recently noted. Huge disappointment *and* a surprise.
I would suggest heading through at the busiest times, so the guards don't have time to kill.