BEagle,
Composite material is more damage tolerant than metal, alternate load paths can be taken in the material at the matrix in which the fibres are in can transfer load to other fibres.
The biggest challenges with composites are with mating to metals (prevent corrosion), and how to fasten them together.
Another aspect which is normally associated with honeycomb filled control surfaces is water injection into the core, which expands as water freezes, and normally results in the delamination of the skin from the core with time.
