Just used CC for our upcoming cruise. The prices were certainly better than I found elsewhere. I ended up going with Cruises-n-more but the agent himself sucked. I couldn't get a quote for the exact cruise I wanted through CC, so I found the cruise I wanted & contacted the agency directly. Although I had to do all the legwork of finding the cruise, the best combination, available rooms, etc...they quoted me $200 less (on an inside) than the cruise line.
As an aside, on CC I only got a maximum of 3 quotes for each of several cruises that I requested. When I filled out their survery after, it appears that there's only about 6 participating agencies total.