For those of you that are concerned about burning calories during a workout (and I'm really not sure why you would be) there is an interesting comparison on this website of a number of workouts and how long it takes to burn 300 calories. Kettlebell workouts come in first at only 15 minutes followed by rock climbing and jumping rope at 28 minutes; swimming (31 minutes), running and cycling (34 minutes) came in next.
I would be curious to know how many calories one of our standard WODs like JAFO or SNAFU burn or even one of our Congressional Medal of Honor WODs. I'm sure they burn significant calories seeing that I am still sweating 60 to 90 minutes after the WOD! :)