I couldn't vote, because no one answer fits me.
Sometimes, I don't have a formal rotation, but I build my schedule around certain workouts (like the Firm BSS4 workouts, which I used a lot the last 3 weeks of December).
At times, I set up a more formal rotation. I just started the following one on Jan 1, which still leaves me a lot of leeway in my choice of specific workouts:
Day 1: interval workout (Cardio Coach, an Imax or Gin Miller's Intense Moves, for example)
Day 2: Full body weight workout
Day 3: Kickboxing
Day 4: 10-20 minutes cardio + lower body
Day 5: yoga/stretching
Day 6: 10-20 minutes cardio + upper body
Day 7: core/abs + stretch
I plan to do that for 4 weeks, then do a "functional fitness" centered week. (But if I see that something in the rotation isn't working well before the 4 weeks is up, I'll change it. So far--4 days in--it seems to be working well.)
At other times, I just do what I feel like doing that particular day, but make sure to alternate cardio and weights, upper and lower body, different intensities, etc.
I've never done a Cathe rotation, because the few I've looked at didn't appeal to me, and I don't like to use just one instructor (unless it's Tony Horton, with his well-planned out P90X series) or too much step. I like more variety than that.
I get back into rotations when I feel like my "just do what I want" system is getting a little bit too lax, or I'm not seeming to get in enough of some modality of exercise.