they still do that in jersey. it's always a good idea to take a look around when leaving a bar at night. very often you'll see a cop parked across the street, waiting for someone to stumble out and get into a car.
I had an email joke a while ago about some cops waiting outside a bar and watching a guy stumble around the parking lot for ages. He finally stumbles up to a car, messes with his keys for some time and gets in. When it looks like he is about to start it up, they dash over and make him do the breathalyzer...he comes up dead sober. Then he tells them he is the evenings DD. They ask where his passengers are and why he was stumbling around. He then explains that DD stands for Designated Decoy.