wow - i am fascinated by this topic. i have witnessed countless crossings firsthand of a person with a dui. ranging from just two people in the car on business, to two couples on vacation, to a large group of dudes for a bachelor party (mine; montreal). on one occasion, there were two in the car. it never came up once; he gave his license/passport, and they waved him right through each time. i can't even recall any but the most mundane questions (any drugs, contraband, etc, where you going, etc).
this was over a range of about 10-15 years ago. has this all changed in the last decade, or was this dude's numerous leisurely and uneventful crossings just an incredible streak of luck?