A step junky's humble comments
Well, I know this is not technically correct but in my humble opinion, there's just no such thing as 'too much step'.
Having said that, it is absolutely advised by many sources, including Cathe, that people should vary their cardio activities in order to avoid overuse injuries as well as providing your body with different types of challenges.
I'm just such a step junky myself and I really can't stand hi/lo. That's simply because I always get cramps, the balls of my feet really start hurting and I also get a terrible headache from all the impact with a floor that does not give like a step does! One thing that's so wonderful about step is that you can have high intensity and low impact at the same time, unlike most hi/lo workouts.
I have been trying to vary my cardio a little bit by going cycling more lately but I find that it's so similar to step in a lot of ways. I'm convinced that I've become much more advanced as a pedaller just because I'm always doing intense step workouts. Many of the same knee rules apply ~ don't go past 90 degrees and don't snap your knees either. I've been trying a little more of Cathe's kickboxing segments too, just to try to round out my work a little, but it's not because I'm tired of stepping!
As far as giving you a bad shape, no, it won't. A stepper's shape is typically quite athletic looking but very feminine as well. Well defined but not beefy looking calves (especially if you 'lift' a lot), round but not bulging glutes and toned inner thighs. I think it's a great shape.