At least twice recently, that I can recall. I was driving, my wife made the calls. On both occasions, we kept police updated with the driver's location. One woman was going over the knoll of hills in the opposite lane - if there had been an oncoming car, there would have been a head-on collision. This was on a curvy, hilly road - she was in the oncoming lane or shoulder more often than in her own lane. I maintained a safe distance, and followed the woman all the way to the road she lived on; gave a complete description of the driver from when I was able to get close - the dispatcher said that they knew who she was, and her address, and a trooper would be along shortly.
Just a few weeks ago, I saw someone almost take out the guard rail on the side of the Interstate nearby, and seem oblivious that they were over there on the shoulder - in this area, the edge of the road has those grooves cut in that make your car vibrate to let you know you've crossed the white line - wasn't just a case of texting, or the driver would have known - he was driving with his driver's side wheels going on and off the grooving. He took the next off ramp, and missed the stop sign. He stopped... completely across the lane of traffic on the next road. Again, fortunately no one was coming through what is generally a busy intersection. We followed him for 3 or 4 miles and they had my wife stay on the phone helping them keep track of where the vehicle was located. It was a college student.