I think KB will complement ALL of Cathe's workouts, including STS. I started KB end of July this year. I stopped all other workouts, and did only KB's. Last week I did PUB and PLB and was AMAZED at my strength!!! I did ALL 5 sets of upper body with my 25# dumbells(except for shoulders, which I used 10#). I had to use my boyfriend's 44# KB to work my lower body because my dumbells weren't heavy enough. Kettlebells work stabilizer muscles which is only going to increase your strength in major muscle groups. So, that being said, this is MY plan for incorporating KB's (which I refuse to quit) into STS:
WEEK 1: STS workouts 1, 2 & 3
WEEK 2: KB's only
WEEK 3: STS workouts 4, 5 & 6
WEEK 4: KB's only
WEEk 5: STS workouts 7, 8 & 9
WEEK 6: KB's only
WEEK 7: STS workouts 10, 11, & 12
WEEK 8: Active rest week
As you can see, 4 weeks of STS will be extended to 7 weeks, but I can only see benefit from this. Just my opinion and what I plan to do! Can't wait, hope 2009 will be my fittest!