Jeff - Any composite will break down in the sun if the resin matrix is exposed. It doesn't matter if the fibers are carbon, glass, kevlar or something else, it is the resin that loses it's material properties.

As far as coming apart from the loading of skiing, it depends on how stiff the ski is and how much it flexes (strains). Carbon is stiffer, so you can use less material and still achieve a durable ski. You could match it with glass, but it would be heavier. The skis that come apart are likely pushing the limit for the loads of whoever is skiing on it. Also, I don't know for sure, but I think a less capable strong skier yanking right off the buoy can load a ski as much as the open guys do...