I bought mine (a Garmin GPSmap 195) for use while flying. Needless to say, this unit was loaded with a basemap of the United States as well as all of the current avaition data;(airports, navaids, intersections, GPS Approachs, andairport information.
For several years I used it almost exclusivly for airnavigation. One year I decided to take the GPSr with me on vacation to the east coast. It proved to be of as much help on the road as in the air. We got lost returning to the resort, so I just fired up the GPS and 'back tracked' from our current position back. It worked like a charm.
I've also taken the unit with me on a cruise ship. It was great knowing where the ship was at anytime, and to be able to track our voyage.
Just lately, I got into geocaching, Once again the 195 is proving to be an outstanding, if somewhat bulky, unit leading to the caches I've found so far. The unit regularly shows EPEs of 20 feet or less, even under heavy tree cover.
But the real reason I bought the GPS was for air navigation. The rest of it's uses to date are just icing on the cake.
Good enough... Never is!!