Airbus has the obsession to use composites in much of the tail in most of its models. Joining a metallic component with a composite one is like asking for trouble. Always. (e.g. see section 19 on the A380). But that is not what is worrying me - I am scared of the 787. Rumors indicate that it actually would be lighter had it been built of Al instead of composite. This is because composite have never been used on such scale before so large safety margins are used to absorb the uncertainty.