Over at the Visual Thesaurus, Jonathan Owen turns his attention to the supposed rule that "fewer is for things you can count while less is for things you can't." After analyzing various exceptions and paying attention to the history of the question and of actual usage, he comes up with a more accurate description of how the two terms are used: "Less is the default, but we also have the option of using fewer when it comes immediately before a plural count noun." His discussion is exemplary: this is how one should think about the rules of language use.
The history of the count/non-count version of the rule is itself exemplary: as Owen points out, "it wasn't until 1770 that Robert Baker suggested that maybe people should use fewer instead of less with count nouns, and the rule has expanded and become more rigid since then." In other words, the "rule" comes not from considering how people actually speak but from someone suggesting that it would be better if people spoke differently.