Also, carbons dampen oscillation better than aluminum.
Properties of carbon arrows aloows 1 spine of arrow to work well with more variables whan aluminum (usually, you'll only find 3-4 spines in a carbon arrow range, vs. dozens for aluminum). This means you have a little more forgivness with carbon when setting up the bow.
As Arthur said, the better carbons are MUCH better than the cheap ones. To that I'll add the BEST carbons are often as good or better than the best aluminums as far as spine/weight/straightness consistancy are concerned. (I have found Game Tracker Carbon Express 3D selects to be especially good in this matter.)

All in all, I feel the carbons are more durable, and last longer than aluminum (If they do wear out.....it SEEMS TO ME that they wear out slower than aluminums.)