So, about the GPS...
I have a really good sense of direction, and I didn't flunk geography. Plus, I have a vague grasp of how the US Interstate system is laid out. Thus, for example, if I wanted to drive from Indy to, say, Dallas without becoming a FOPA test case on some roadside in Illinois, I would nav my way from Indy to Louisville and thence to Nashville, Memphis, Little Rock and on to the Big D.
Even if one doesn't know the numbers of interstates, this task is facilitated by great big signs hanging over the road telling you to which city this road will take you. Is the city between your starting point and your destination? Then you are on the right road.
So when I bought the GPS, it was mostly because they'd become cheap enough to make a decent roadtrip toy, with their running Time-Speed-Distance display and calculation. If nothing else, you could make a game out of trying to shave time off your projected ETA.
But I did discover one thing for which they're very useful, at least for me. Whizzing into an unfamiliar city, headed for an unfamiliar spaghetti bowl of entangled interstates, having Robby the Robot prep you ahead of time for your exits and lane changes is handy. Instead of having to read signs and try and psychically figure out which lane you're going to need to be in to get from I-65 South to I-40 West, while simultaneously dodging the drooling morons that make up urban freeeway traffic these days, you can now let the Auto-Nav feed you the correct lanes while you concentrate on moron-dodging. That's handy.