what exeactly are you going to be cutting that is cf? Is it a flat piece, is it rounded like a fender? Like Duckets said, where a Mask. But if the piece is flat, you can use a jig saw and a fine toothed blade for metal work. Ive heard some people tape over the carbon fiber with masking tape then draw cut lines ontop, not sure if this is absolutely neccesary, but worth a try i would think. A dremel would be needed for more complicated cut such as curves, if using a dremel, buy the Diamond Wheel part# 545 or the carbide cutting and shaping wheel part# 542. Take your time and check measurements before starting the cut and im sure you'll do just fine.
Thanks all for the posts. I had a CF rear hugger that wa slightly warped. Pain in the a$$ as I would constantly think my rear wheel was misaligned. So I finally cut it down yesterday. Got some high rated dust masks and went to work with the dremmel. I first used masking tape and drew some rough lines of the relative shape I wanted and then went to town (by eyeball only using the center mount as the center point). Overall came out better than I though it would. Sanded it down and its pretty smooth. Only thing that sucked, was I slipped with the dremmel a few times which resulted in a couple of small scratches, oh well I'm not that picky. Going to mount it on the bike today to see how it looks on the bike. I'll post some pix soon.