A while ago there was some controversy about an article suggesting libraries have a rating system on books to help parents discern what might be good or bad for their children to read. I definitely find myself agreeing with the ALA on this - that libraries rating books is a form of censorship.
Public libraries should not endorse stopping kids from reading certain books. That responsibility - deciding what exactly is appropriate for a child of a given age - belongs with the parents of that child, not to mention the impossibility of giving an actual sweeping generalization of what's appropriate and what's not. Every child is different, and what's okay for one eleven-year-old might not be for another.
Of course, there are ways for parents to see ratings for books if they so desire (websites and the like), but these ratings should not be something sanctioned and endorsed by the library. They should be private resources for parents who want to follow them.
What do you think of the idea of rating books?