I have a 2010 carbon Cannondale. It's really light (18 lbs) and comfortable to ride. I'll take it to the mountains to ride, if I ever get back in shape.

Our choices are determined by what the manufacturers produce and market. AL frames were the rage for a time - lighter, stiffer, etc. At the moment, carbon is the preferred production material. Is it a fad? Who knows. Carbon seems to integrate the lightness of aluminum with the comfort of steel. Haven't heard of any "asplosions" lately. Will CF frames stand the test of time, like steel? That remains to be seen. Steel is still an option for new frames/bikes: Ciocc is still building and selling steel frames. All the new Colnagos I see are CF. Same for Pinarello.

Carbon won't rust, that's for sure.