Hi Karen! I LOVE Jennifer Kries pilates. I noticed a definite difference in ab definition and flexibility. As for her yoga, I have one of her "advanced" power yoga dvds and I wouldn't QUITE call it advanced HOWEVER its not easy and is very relaxing. I usually go Bryan Kest power yoga, which is definitly advanced, when I want a hard yoga workout (the cds are usually an hour and half). But when I have less time and more want to relax and get centered I go for my Jennifer Kries dvd.
Hope this helped!
-Lauren