Yeah, I thought it sounded like it might be a high estimate... but all I had to go on was her little interview segment on the DVD.
Still, like you, I put a ton of work into it. I keep up with her pace and often do extra arm exercises during the "boring stuff".
Still, even at my lowest estimate, of around 400, its a very good workout for me! Two weeks ago, I had trouble getting through the first mile of the workout (on the Power Walking System DVD, which seems a bit more exercise than the 1, 2, and 3 mile VHSes that I have), but now I can easily get through all three miles, do 60 sit-ups, and continue onto the 1 mile VHS. It's nice when you start getting energy back! Plus, my DH is starting to get jealous! He sees me work so hard to exercise, so he joined a gym to keep up with me!