I've been doing it for a while now - although I find it very difficult to get all 6 days in - I just don't have the time sometimes, or you get a little ill, or feel crappy or whatever. But, I am sticking very tight to the weight workouts (it's the cardio and yoga days I generally miss). My strength is definitely improving - I'm up to 80 pushups in all their variations on the Chest, Shoulders and Triceps and for the first time ever I can do push-ups from my toes! So that's cool. I really like the yoga workout and the plyo and the core. I don't like the ab section at all - I find the moves very uncomfortable, so I sub in Cathe's CoreMax sessions for those. I actually got a little stiff from the legs workout, but legs are my weakest area. I will probably start subbing in some Cathe cardio soon, as I'm beginning to miss her. :-(
I do think it'll be great preparation for STS.