You'd have to be pushing 250-300 watts an hour to burn that much, but people do burn that much in an hours time if you look around a few bike forums. If you have time to do a long and leisurely ride, 3 hours or so, the length of the new Avatar movie, you'd probably knock out at least 1000 calories imo. Whats nice about a road bike in particular for caloric burning, at least in my experience, is that it makes you want to push the bike and go as fast as you can and keep snapping up through your gears and catch up to the cars (passing them even when they hit traffic or you are descending).