Wood vs metal - I tend to agree that a ball hit on the sweet spot will have about the same exit velocity with either bat material. The huge difference is the hits towards the handle and end of the barrel. With the increased sized sweet spot, there's an creased risk for injury with metal bats.
Performance - some of you have mentioned how little Johnny's daddy wants him to look good and metal gives him an edge. My counter to that is IF they only have wood to use, it's all relative. Little Johhny will still hit it further than his teammates, just not as far as with metal (in some cases).
I had one more point but work interrupted my train of thought.