I agree with pretty much everything CTN posted...except for the above, and that is only because I have seen first hand that it is not always true.
I had a customer come in to the shop with a bass that was custom built for him. The bass had a fairly thick birdseye maple neck that had an extreme amount of upbow. Even the headstock was warped. You could also easily flex the neck back and forth by hand. It was clear to me that this piece of wood should never have been used for a guitar or bass neck. I know the builder (used to work with him) so I sent him and email and some pics. He was surprised by the movement of the neck because he had used 2 graphite rods to reinforce it.
I guess graphite can be a great stabilizer, but it won't make a bad piece of wood useable, and I'd personally never use it on a standard guitar or bass.