I checked into a carbon fiber tripod a few years ago and back then the main concern was rigidity. Carbon fiber is fexable and as such is not as stable as metal... back then that was an issue.. hopefully they have somewhat corrected it.
Use really has a lot to do with it.. if it is for studio work wieght really isnt an issue.. if you are into nature weight is definately an issue.. if you are talking about something that is mobile but you are shooting sports.. keep in mind almost all large sporting venues dont allow tripods.
My personal feeling on carbon fiber tripods is that they are a good comprimise for nature photographers who need a platform when out in nature and on long outings but are concerned about wieght and mobility.... studio photography is much better suited for the most stable ridged tripod you can get your hands on. If you are talking about mobile but still only from car to a close by destination I'd still opt for the stable platform. If you plan on doing a lot of touring/travelling the carbon fiber, due to its wieght, would be the way to go.
At the end of the day I opted for a monopod
Canon 7D + 50D + EF 100-400mm f/4.5-5.6L IS USM + EF 24-105mm f/4L IS USM + EF 100mm f/2.8L Macro IS USM
Pelican // Black Rapid // Think Tank // Manfrotto // Garmin
Reflections On Canadian Wildlife