Yes, quite a bit, including Professional space-application and military motors, 'professional' consumer motors for the hobby (reusable and SU), and 'amateur". And I'm sure all three have been done before with CF instead of fiberglass.
Like any engineering decision, there are strengths and weaknesses. The strength if obvious; composite cases offer low case mass for a specified design pressure. The weaknesses are many: anisotropic (meaning it's much, much harder to design them to survive a given pressure), lower temperature tolerance, harder to manufacture, harder to inspect and clean after use, more vulnerable to stress concentration problems at snap ring grooves or pin holes, probably more expensive in the long run. Also safety-it's much harder to predict how exactly they will fail, they make shrapnel when they fail, and the shrapnel probably won't show up on an x-ray image.
I imagine people have said all that already, however.
EDIT: Jesus Christ, they tried to cut your head off! Sucks bro. 15, right? I assume you're either in high-school physics or will be next year, right?
It's a bit tough to explain the theory without background, but suffice it to say that when it comes to calculating how strong a piece of metal or plastic is, it simplifies everything enormously to assume that the fundamental material properties (like breaking strength or 'stretchiness') are the same regardless of what direction you measure them in. In general, that assumption isn't possible in composites, where properties of the resin and the fiber are different and the fibers have discrete orientations. That makes making composite cases the 'right' way much harder. That, and the fact that they can't be as easily cleaned, inspected, and reused, is probably why you don't see too many around. I've made some big ones that we never tested; PM me if you want to know more.