Estimating range with a GPS
I've wondered about this issue while I've been out hunting with my Garmin 60CSx, since I've felt the need and also have a background in GIS. Sometimes I could do a decent job because I was looking at a craggy peak or other specific landmark. As for meadows, I eventually added outlines of them to custom topo maps I created for my Garmin.
I've been able to come remarkably close estimating range just by making it a practice to look at known objects from a known distance. I know it sounds silly, but I have a 67' Bug parked behind our garage and by measuring off 300 yards down the alley in 100 yard increments and repeatedly looking at it from those distances when out walking the dog, I trained myself to know what something 4-5 feet across looks like at each distance. I'll probably by a rangefinder someday but that just means more weight and one more device to keep track of and not break. And time to get a shot off is sometimes awfully short.