The Consumerist has a post on those California cancer chemicals warning labels.  Generally speaking, the warning labels encourage a certain level of public safety, but in actuality, their purpose is mostly litigious.  One negative side effect of the abundance of these warning labels is a general disregard for them. 

Warning labels that warn against any infinitesimal risk are essentially useless. The outbreak of warning labels spawned by Proposition 65 is so widespread that consumers are being conditioned to ignore them. Even if some of these labels are trying to warn us against a legitimate risk, we are likely to ignore them since these labels "cry wolf" more than they protect us.

It seems that there's a danger in overwarning.  Too many warnings with too few observable effects (i.e. getting cancer from one of these products) is a bad thing.