I am not sure exactly what kind of carbon fiber they use in bikes, but carbon fiber is like the stuff they use in graphite fishing rods. It is merely a bundle of very thin carbon fibers. They are quite strong and light weight. They are used in forks because they tend to lick up road shock better than other materials. And they are used in many rear triangles for the same reason. The major disadvantage to carbon fiber is catastrophic failure. Metals tend to bend when hit really hard. Carbon fiber just snaps and that is not a good thing to have your bicycle do. However, the engineers have pretty much gotten around the material's defects and there are very fine bicycles made competely out of carbon fiber.