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I see something like P90X as a good base foundation and part of a block training system. It helps break up the boredom of a training year. I used to be about getting as big and strong as I could...then I started thinking along the lines of "what would be a good build for a hunter/gatherer?" (and that was before ever hearing about the paleo diet). I reasoned the type of build women prefer in men was built into their genes, that too bulky was a lousy hunter/protector/warrior in a paleolithic tribe. I figured that build was healthier in the long run too. (Personally, I always preferred a Frank Zane build to the bigger bodybuilders of his day. I'm giving my age away, now).
If a person simply wants to have good muscle tone and not be "too" bulky something like P90X isn't a bad way to go, esp. if you workout by yourself. I add more weights to it, though. I do squats instead of the back/leg workout. While it's alright for upper body P90X is weak in the the leg workout.