Aren't most PCBs made out of fibre glass material? Do you think it would be possible to use a carbon fiber board for surface mounted components?
If so, they might be planning to put their components right onto the outer shell itself (on the inside of it thought) That would make for some seriously thin products, especially for the iPads and their smaller gadgets.
Carbon fibre is conductive as far as I know, so it's not a good surface for mounting components.