Sorry to dig up an old thread, but the data shared in here is pretty inaccurate so I'll set the record straight . . .
1) Carbon was first appeared bikes in 1975 with the Exxon Graftek road bike, but this was highly experimental technology and it took about 10 years before folks like Craig Calfee, Brent Trimble, Easton, Yeti, Look, and later Trek started building their first bikes with Carbon tubes. In the late 80's and early 90's when the first carbon off road frames appeared the technology was still very much under development and not well tested so lots of failures occured.
2) By 1995 several top carbon makers had "figured it out" and learned how to make great carbon bikes, but there were also a lot of badly built carbon products still being made. It's just like comparing a department store steel bike with a well built cromoly frame. You can make a great bike or a bad bike out of any material. It's not just the material - it's the design and manufacturing that matters.
3) Since about 2000 there have been several companies making "Downhill" racing frames and components out of carbon fiber. Clearly if these DH bikes which sometimes hit speeds over 50 MPH are subjected to even harsher stress than BMX conditions are successfully using carbon, then there's no reason a good BMX bike couldn't be manufactured in Carbon. It's more a matter of cost. Historically carbon has been more expensive to manufacture because it requires a lot of labor and the material is also more expensive than steel tubes. This is due in part to the ever increasing demand for carbon by the Auto and Aircraft industries which are building more and more in carbon. Carbon is also heavily used in the boating industry. Carbon is "ideal" as a material to be used in water or outdoor conditions unlike steel which suffers from rust problems. Sunlight can affect the longevity of some composites but this problem has largely been solved by new glues and finishing that protects the fibers from UV damage.
4) Carbon manufacturing is getting better and better by the day and costs for parts of the process are beginning to drop as the technology has become more and more popular (although 2005 had a bad "carbon shortage because demand for the material was higher than the factory supplies driving costs up - this is a temporary problem while demand is increased).
6) One of the biggest advantages of carbon construction over steel or welded bikes is the ability to create optimized structures and shapes in designs that put more material where it is needed most and remove it where it is not needed. It's not easy to make a metal shape in anything other than a round tube easily and cheaply. With carbon it is much easier to create unique shapes and create strength by adding thicker layers and fiber alignments in areas that require more strenth while keeping other areas very thin and light. You just can't do this as easily or effectily with metal. In addition without getting too technical, the structural/strength properties of carbon far exceed steel so you can create a stronger bike.
7) The one caveat is carbon failure curve is very different from steel. Steel's properties allow it to bend when it begins to fail, while carbon is much more brittle and when it reaches a ultimate failure threshold it snaps rather than bending. This means that you need to design carbon parts with much higher safety thresholds or "overbuild" carbon products to ensure this doesn't become an issue. Even with overbuilt safety cushions, you can still build most products lighter in carbon than in steel or aluminum. Aluminum also fails similar to carbon in that it snaps rather than bending much, so it shouldn't be assumed that "aluminum is safer".
8) in conclusion, carbon is an ideal material for building performance oriented BMX bikes and parts and will grow in popularity as the price continues to drop. It's no longer a question of the technology being capable to withstand the stresses. This challenge was solved a long time ago and is proven in DH and aircraft industries where failure testing and stress levels are way higher than BMX. The real issue is the economics and also consumer perception. Carbon has gotten a lot of bad press and misinformation has been spread over the years because of early failures. Remember steel bikes been manufactured for over 100 years so there's been tons of time to perfect the design and building process. Carbon really got it's start around 1987 when multiple builders really started pushing the material so it's advanced pretty fast but, it did take some growing pains to get there.
For more on the history of carbon in cycling visit:
www.carbonbicycles.com
-mtnwing