I totaled 2 aluminum frames in ~4 years of daily use (down tube weld failed both times). Trek offered me a carbon frame with the proviso that they would not replace the frame again. While conventional carbon fiber is more suceptible to impact damage, I am certain that this frame will never fail due to normal wear and tear.

PS: I should note that I have also broken steel frames -- cracked head tube and cracked stay near der hanger. (The steel frames, however, lasted many years.)