I have a GPS, but I back it up with paper maps. The only real issues I've had with the GPS are the fact that it sometimes attempts to send me down streets that aren't built yet (they just don't exist yet) and streets that are incomplete for a certain section.
I drive a pretty heavy truck, so I just figured out how to get my GPS set so that it won't plan a route for streets where trucks are prohibited, send me over any weight restricted bridges, send me down alleyways, put me through a one lane covered bridge, or any route with height restrictions. You can set the GPS to optimize the route for a truck, and make it so that you don't have to do a U turn when it recalculates. That's been a blessing since I realized that you could set it that way.