Barry, I do the same thing sometimes in my workouts. I may do push-presses or something similar, and start out with 15 reps, rest 10 secs and do 8-10 reps, rest 10 secs and then do 4-6 reps, while increasing the weight each set. This is based on Art De Vany's evolutionary fitness model, and I like the concept a lot.
Michael, I do the same thing often. I don't see a problem with it at all.