I think on a bike you're looking for a seatpost mounted rack is the way to go. Anybody who has much experience with carbon bars knows that Carbon is beastly strong when used as designed but it's really easy to crush and ruin it by over tightening your levers. You could be careful with the p-clips and be OK there but it's tough to know what the load on the side of the tube is going to do to the carbon tube.
I've got a super-light old Aluminum road frame (Alen glued-and-screwed) that I was thinking of mounting a rack to with p-clips but then decided it was a bad (or at least risky) idea. I like the frame and don't want to ruin it. I would guess you'd feel the same way about your new $1000+ carbon frame!
edit: oops, missed that you already bought a bike. My comments still apply.
Chris
Last edited by GV27; 07-07-08 at 10:31 AM.