I'm with Doug on this one, and primarily because I spent my entire adult life working with "the motoring public." I can tell you that the majority of those folks can not even operate all of the basic controls on their superduper all automatic cars. Let the automatic headlight dimmer go belly up, they don't have a clue how to dim the lights themself. Have a truck overturn blocking the off ramp they take to work every day they are lost, because they do not have a map of the city (Los Angeles in this example) they live and work in. Show them your Thomas Guide and they look at it as if it is written in Greek. Tell them to go north so far, then turn east, you get a blank look. So you make it simple and tell them to go "this way" (pointing) so far, then turn right; half of them will look left.

Using a map and compass to navigate is a skill that needs to be learned and practiced often, and the majority of "the public" are not going to do it, no matter what. If they don't have a map of their home city, they are not going to buy one of the area they will be in for a few hours/days/weeks. I recently had to spend $11 for the topo of the area we are currently in, primarily because I love maps, but also needed to refresh my use of map and compass, and wanted to try using the UTM feature of my GPS for the first time (I like it). John Doe Public isn't going to do this. So, if having a GPS only helps 50% of the users, I figure it is a good deal. But I suspect that the average number will be higher than that...