Thanks for the replys so far chaps. I too have been reliably informed that carbon brakes are an option (albeit an expensive one) to be retrofitted to the B737NG.
They would obviously provide savings in delta burn/ fuel flow due reduced weight, but does anyone that has operated with them know if they provide improved field length limited performance figures for takeoff and landing? I assume this would require further test flying (expensive) to validate, but would be the only financial reason strong enough to convince the operators to spend the money retro-fitting them.