Durable generally means well built components that aren't super light. For xc racing a lot of people make sacrifices in durability in order to have an extremely light bike. Some examples are extremely light tires and tubes, light rims, spokes, chains, cassettes, chainrings, bolts, etc. A lot of these parts won't make it through a season, therefore they aren't particulary durable.
In most applications carbon is durable. There are exceptions of course and no need to debate it. There are plenty of threads doing that already. I have had my carbon crankset for four seasons now. You just have to use your best judgement. For example I have no problem using a carbon seatpost on my roadies but I'm afraid to on my mountain bike. For that I'll use a Thomson Masterpiece.
__________________
I may be fat but I'm slow enough to make up for it.