Read something interesting about the creator of P90X, Tony Horton, in the NYT article The Fitness Revolution Will Be Televised (After Leno): The buff fitness guru "rarely eats meat or drinks liquor or coffee."
On his blog Tony states "I was vegan for years and recently I added free range chicken and wild salmon." So at least he's not a gung-ho Paleo fanatic. He also has a post by his vegan chef Missy Costello about nutrition.
Tony's main point is to "eat HEALTHY FOOD!" and I completely agree with that. Too many diets start with a narrow philosophy and then ignore good nutrition.