I am going to make a prediction. Yeah, I know, stop the presses! Look at this:
This 'spy shot' of what looks to be a composite Specialized 29er hardtail will be making its way around the net I imagine. It looks poised to join the GF version of the same approach.
I would not be surprised if the Specy is a more durable frame then the carbon Gary Fishers have been, but that is just a speculation on my part. It seems like the Big S designs a bit more to the sturdy side of things and it would be smart to let the battle of the grams scale go to Gary F. and win the war of durability and trust among riders. But that is not the prediction I mentioned.
I predict that over time, carbon frames will be what most serious riders want to pedal. Cost will come down to the point to where a nice aluminum frame is now. Ti will still be the king of bling and longevity, but it will not come close to the performance of carbon. Neither will aluminum and certainly not steel.
Why? Look at the shape of the tubes on that frame. Now add in the ability to go way beyond what can be done with a metal tube/shape, such as butting or hydroforming. The way the layers of fiber can be constructed to provide a certain pedaling and ride performance seems to be such an advantage that I cannot see metal getting there without costing a great deal, if it can be done at all.
I have never really considered a carbon frame for off road riding. I imagined them too fragile, too chi chi, too odd. Then I rode a couple of nice carbon bikes for a little bit. The pedaling performance was amazing. Stiff BB, fast response. Light bike. Look what it has done for road bikes. Why would I want to buy a non carbon road bike other than some bow toward the 'steel is real' emotion or the cache of Ti? An aluminum road bike? Do they still make those?
I imagine cheap carbon is like any other cheap bike...not so great. But the potential of carbon seems so wide open that it has to be a matter of time before I will be shopping for the next 29er. A carbon fiber one.