Today i did a 34 mile ride with 2000 FT of climbing and burned 1039 calories.
The reason i know the exact amount is i wear a bodybug like on biggest loser, so far i have lost 101 lbs and am maintaining it for the last 4 mos.
i also weigh most of what i eat (A little over kill but that's just me)

500 calorie deficit a day = 1lb weight loss a week
1000 calorie deficit a day = 2lbs weight loss a week