I travel with a couple different GPS units, a Garmin Nuvi sits on the dashboard and provides the highway routing, traffic avoidance/optimization and ETA info. I routinely ignore its advice in the local area because I have preferred routes and I like hearing it say "recalculating"

The other GPS is a Garmin GPSMAP 60 CSx. It has routing ability but I never use it. It is loaded with terrain maps of the western US in addition to standard highway. It also gives elevation info which for some reason is unavailable on the Nuvi (unlike the GPS V which I used before the Nuvi).

GPS receivers are great for navigation, but you need to know their limitations. I'd never follow the Nuvi offroad.

That said, shortest distance does not equal shortest time; my Nuvi's routing is set for shortest time so it almost always generates a route on highways. (Edit: a Nuvi can be set for shortest distance, but why take the shortest distance if it takes more time??) If it ever put me on a gravel/dirt road, I'd be pulling out the Rand McNally Road Atlas to see where on Earth I was.

I also travel with a PLB.