There's an interesting article in Bicycle Retailer and Industry News (BRaIN) about the possibility that carbon fiber could become the dominant choice of materials for full suspension mountain bikes. (Just noticed the article is old, despite it showing up in my feed reader for the first time). The article cites the fact that major manufacturers such as Giant, Scott, and Specialized are having success with their carbon fiber, full suspension frames and implies that the mountain bike market will follow the road market that has embraced carbon as the high-end material of choice by consumers.
If true, this may have a negative impact on smaller niche manufacturers that produce high-end aluminum full suspension bikes. Here's Santa Cruz's president Rob Roskopp on the likelihood of this happening in the near term:
Compare the cars road bikers drive and the type of car a full-suspension guy rides. Road riders put their $7,000 bike on top of shiny $50,000 cars. But the average full-suspension rider puts his $4,000 bike on top of a beat-up barely-hanging-together car that costs a fraction of what their bike costs. For them their bike is their life.
Gross generalizations aside, I'd have to agree that if the price of carbon fiber doesn't come down it will always remain a high-end niche product. I will say, however, that carbon fiber should be the material of the future. If you've ever ridden Cannondale's Rush Carbon or the Trek Top Fuel 98 and compared them to their aluminum cousins, the ride is much smoother.