According to the Guardian, several British authors spoke out at the Hay Festival about the plans for some publishers to begin labeling books with age ranges.  Mal Peet spoke out for reluctant readers and its impact on them.  He also brought up my main concern:

According to Peet the complicated question of whether the books are suitable for children of a certain age in terms of language or in terms of subject matter is "not being addressed at all."

"Sooner or later this age ranging is going to degenerate into a moral code," he said, "which would be terrible."

It certainly would.  Think of teen novels in particular and the age labeling that could happen not on the basis of reading difficulty but of content.  And who decides what is and is not appropriate?  Another hidden panel like the movie ratings?  So nothing can be done?

We recently had a challenge to a couple of books at our public school.  One "solution" was for the librarians to label books with ages.  And this was not for reading level, but solely for content.  When publishers start thinking along the same lines as censors, there is something wrong.