Carbon frames are fine for anything other than downhill. There are plenty of videos out there showing how carbon is stronger than aluminum in just about every aspect. Yes, they are more prone to breaking if you hit a rock at an off angle, but they are much less likely to crack at the junctions like head tube to down tube, seat tube to top tube where an aluminum frame has welds.
Certain bike manufacturers will give you a lifetime warranty on a carbon frame as well - ie Specialized and a few others. I would pay more for a carbon frame from a company that offers this warranty if it was a carbon OR aluminum frame.
Don't buy into the aluminum last forever stuff either. If you push any bike to its limits and beyond, you will eventually break it. TJ had gone thru 5-6 aluminum frames and he is in the Hall of Fame. I think it is safe to say he is a better rider than all of us put together.
SM