I find that my calories burned varies greatly depending on the type of workout I do.
I wear a heart rate monitor, that is set specifically to my height, weight, age, sex etc....measures my heart rate as I work out and calculates calories burned. When I run or cycle I burn anywhere from 450 - 550 calories an hour. Weightlifting is significantly less - but then my heart isn't pumping continuously then either.
Sorry to say though, you can't always *trust* the calorie counters on treadmills/ellipticals etc. They simply don't have enough personalized info to be accurate.....