Have owned C5 V6 for 4 years now with brake squeal a regular occurance. Most effective fix I have found, providing all braking components are in good order, is to apply heavy braking pressure when stopped at lights etc. Also to apply regular strong braking action when safe to do so when approaching need to stop/slow down. This also seems to alleviate to a certain extent the brake squeal usually heard when in reverse. Living in city and driving an automatic I naturally tend to use brakes lightly, sometime heavy use appears to keep calipers 'active'.
