Just back from a quick "out and back" ride with Endomondo tracking. The return leg is exactly the same as the outward leg, except in reverse. Endo stats:
OUT:
Average Speed: 23.4 mph
Calories: 638 kcal
Distance: 13.00 miles
Duration: 33m:17s
BACK:
Average Speed: 17.4 mph
Calories: 576 kcal
Distance: 11.74 miles
Duration: 40m:25s
That's a discrepancy of 1.26 miles! Does anyone else see the same kind of variability? Is it the software or is it the GPS receiver on the phone (Desire S)? Is Endo Pro any more accurate/consistent?

