As I understand it, most of the "Horror stories" are caused by people that were not prepared. Have all of your papers in order when you get to the window, be polite, and don't act nervous.
Regulations are in flux right now, I'd be checking regularily, and espescially as the time aproaches.
I had a bad time at the border going into the US at Detroit one time ( before 911), because one of the jerks I was with forgot his ID. Tore the car apart, dumped our luggage, put us in a cell for half an hour. Nice welcome.