I hate GPSs, refuse to use them, still navigate the old fashioned way with maps.
A few months back, I went to another city on a day trip with a client. On the way back to Montreal, there were 3 bridges we could cross. She had a fancy GPS that was plugged into the traffic network so the GPS could route us where there is less traffic. The GPS was routing us towards one bridge that had much less traffic going into town than the other two. The route looked a bit strange, so after I inquired, I was able to point out to her that that bridge was a one way leaving town during rush hour, meaning we would not be able to use it for another 3 hours.
