There was a fiberglass glider in the UK hit by lightning several years ago and it simply exploded. The moisture in the fiberglass turned to vapour and split the thing apart. Both people parachuted safely.

Though obviously this not the same fiberglass process as the airline manufacturers use.

The story of the glider went into an AAIB report, complete with pix, on the investigation of a Super Puma ditching after losing the tail rotor. Very technical investigation on lightning resistance and they found, as FC mentioned, composites have very high resistance to conducting electricity, but when they do, things fall apart. In this case the metal strip on the blades couldn't cope. The only reason they did not all perish, and managed to autorotate, was that the tail rotor assembly was held on by the hydraulic line.

AAIB then recommended far far higher standards for lightning resistance as the load which caused trouble in the north sea was tens of times stronger than the worst case scenarios devised when designing the lightning standards. Nothing has been done though, despite greatly increasing use of composites.