gw_12 (whom I like to call geek_12) over on bikejournal sent me this explanation of GPS-only elevation gain/loss problems:

Consumer grade GPS is just not very good for accumulated elevation measurement (that’s why survey grade GPS units still cost about $5000). As you probably know consumer grade GPS can be off in the horizontal plane by 5-10 meters or so at any time. In the vertical plane they can easily be off by 2 to 3 times that much. While that drift in the horizontal plane may not produce an unacceptable error in the distance measurement of a bike ride (lots of horizontal travel vs relatively small errors), 2 to 3 times that error in the vertical plane over the same amount of time and much less vertical travel makes the accumulated elevation data practically worthless. Note that the indicated elevation is typically with 50 feet of actual, but varies over the ride from -50 to +50. The system has no way to discriminate between actual climbing and descending and error drift.
I, personally, have experienced gain/loss data 3x the actual with the Forerunner. So the deals to be had on the Edge make it worth having both.

The FR has been useful to Izaak the Wonder Poodle as he is currently racking up the mileage to the coffee shop and back. And I'll use it for snowshoeing once we move to Bend. It will definitely come in handy. Besides, I'm sure that yellow has dreams that someday she'll convert me to trail-shuffling.