Composite gliders have been around for over 40 years with an excellent
record for structural integrity. My Glasflugel H301 Libelle glider,
N301BW, will be 40 years old in 2004. Made of plain 'ol E glass and
epoxy. Closing in on 3000 hours of flying time, still looks and performs
great. Very few AD's, all on the metal parts.

I have owned and flown old wood, old metal, and old glass. I have had
more problems with the metal than the wood and glass put together.
Corrosion and fatigue. Probably because people are more likely to take
care of wood and plastic and to neglect metal. Fabric covered aluminum
wings are probably the worst for this. Often left sitting out for years
with moisture collecting in wing, not to mention rodent urine, etc. Seen
aircoupe spars that were little more than aluminum oxide powder.

One thing about old glass: Old fiberglass aircraft were significantly
overbuilt to get some rigidity out of the very flexible fiberglass.
Hence, my glider has a 9.5 g wing just to make the wing stiff enough to
keep both tips from drooping to the ground when it's not flying. Carbon
is stiff enough that you can build a stiff structure that is still
pretty weak.

Composite materials tech and fabricating methods are advancing at a high
rate. Eventually, new metal airplanes are going to get rare (says the
guy who just bought a bunch of steel tubes, rags, and sticks with a late
40's Continental to drag it through the air).