I've been experimenting with CDC for a few years now, initially motivated by Hans Weillenman's 'CDC elk' troutfly and it's bonefish variant that showed up on globalflyfisher a few years back.
I've got several flies that use it now and am pretty happy with them. Typically, the CDC is palmered to give the fly body, much as on a CDC elk.
The big thing is ability to vary shine by wetting out a fly. On a dry fly, CDC traps air bubbles and gives it a lot of body and shine. It works well, but the cool thing is the ability to get rid of much of the shine by wetting the fly in your mouth.
When a bonefish refuses, oftentimes the trick is to throw it something rather different. With CDC, just wetting the fly with saliva gets rid of much of the air and presents a MUCH less reflective fly. Oftentimes, this gets a hit just seconds after refusal.
I've worked the CDC elk into a squat crab fly and a couple light shrimp imitations as well, and would strongly suggest experimenting with it. It's also wonderful for cushioning landings on tailing flies. If a wet fly is spooking fish, a few quick false casts (away froim the fish) will dry out the CDC and get you a much softer landing.
(Jim Miller, you are no longer sworn to CDC secrercy.