I think the biggest problem people have with the map is that it isn't really a map at all: it is literally a scaled version of the dungeon itself. So it's very 3-dimensional, so you do have to move the camera up and down to follow stairs and ramps, etc. The view distance doesn't help either, as there's a pretty narrow range of height where the map will actually show something.
But really, other than reviewing the immediate area, the map is most useful for 2 things: (1) looking for hidden doors. They may fool you, but they'll never fool your map. Just pop it open before you leave a room and you'll see if you missed something. (2) the micromap, just so you can have an idea of where you are relative to the exit, or when you have left one dungeon block into another. Other than that, large scale retracing of your steps on the map or scouring for a missed passage isn't easy to do.
@Python: Yea, I totally agree about water areas. I hate them, even with all the luxuries of water walking/breathing, I'll often just turn around and say good riddance to your silly mummy wrappings.