Well, before my wife joined Curves, and I started working out at work, we both used Power 90. I only did the cardio dvd, so I will comment on it:

It's about 40 mins of cardio, with small breaks in between so you can catch your breath. First you do some stretching, then you move into power yoga, which is very good for stretching, etc...but I can see this being a little awkward for people that are significantly overweight. In my opinion that would be the only negative about the cardio tape.

In all, the cardio tape does it's job well, it will make you sweat like a pig.