yes, the numbers here seem high... i was chalking that up for an estimate for the "afterburn" effect that is mentioned in a number of recent works... where after a run our bodies burn calories at a higher rate than basal metabolism. even at faster speeds, every other calorie measuring device that i've used (hrm, treadmills, etc) says i burn well under 100 cals per mile, whereas here at fitday it's always more than 100.
and sure, i agree that the calculator here is just for an estimate. just like in running, for instance yasso 800m intervals can estimate your marathon time, but it's always been less than my marathon time when i've done them. i'm to find out how close it is, and use the food journal to see patterns in my eating, and then tweak them.
kimmy: as a runner in the desert south-west, i know that the scale numbers are quite variable! not only is your body composition change reflected by that number, but hydration level too. during the summer i can fluctuate 10-15 lbs a day as i lose and then replace a gallon of fluid during/after a long (2-3 hour) run. long term trends in my weight over a week or more are the only way that i can really see how my body weight is changing, and you're right that more detailed analysis is the only way you can measure composition changes.