First of all, have they ever provided enough stopping power? If not, then upgrade. I remember someone on this forum mentioning that the Cane Creeks were "flexy" and that they didn't have quite the power of other brakes. I don't remember if they were speaking about your particular model, though, and I have a friend that swears by them.
Okay, so then, if they have provided enough power in the past, there are a few things to do. First, replace the cables and housing. That always seems to help many issues, whether brake or derailler related. Second, check how worn your pads are, replace if necessary. Third, make sure the pads are making maximum contact with the rim. Fourth, make sure that both of the pads are contacting both sides of the rim evenly, i.e., at the same time. If not, depending on the brake, there will often be a little screw that adjusts this on the actual brake body. If it's way off, though, you may want to check to make sure your wheel's hub is seated in the dropout correctly. Another thing to check: Make sure that your brake body pivot point isn't sticking when you release the brakes. Lightly lubricate if necessary. (NEVER lubricate the pads, obviously). Make sure your rims and pads are clean.