hsballcoach- With respect to gaining explosiveness, I think Insanity's major flaw is the lack of rest time. Shaun T takes high intensity interval training to the extreme here, and it is very difficult to continue each exercise at 100% effort through the entire workout. I had to continuously take breaks throughout each portion and very rarely was able to keep up with the instructors. As a result, the explosive nature of the program was somewhat lost because I was not able to continuously put 100% max effort into each exercise for that extended period of time. I don't doubt that the exercises in and of themselves promote explosiveness and athleticism, but in the overall context of the program I think it is lost because of the sheer difficulty of the workouts all combined.
When I complete plyometric circuits in my own training, I implement several of the Insanity and P90X movements in my daily routine. This hybrid combined with the weight training that I complete for baseball is, in my opinion, a much more ideal workout for the sport-specific nature of the craft.