I think it really depends on a lot of things- your age, height, weight, fitness level, how hard you're working, how much you 'phone it in' etc. It's probably different for every person. I usually wear a HR monitor that gives me a good estimate of calories burned. When I was doing Jillian's Ripped in 30 (similar in length/format to 30 DS) I was burning 250 calories per workout. Still pretty good for 1/2 hr.
"Blessed are the curious, for they shall have adventures" -Lovelle Drachman