Of course the first thing that springs to mind in the UK when discussing the banning of books is the notorious 'Lady Chatterley's Lover' trial, when in 1960 an attempt was made to ban the book under 1959 The Obscene Publications Act. As with most such events it was a case of all publicity is good publicity, and the book was probably far more widely read as a result. Similarly the autobiography 'Spycatcher' by Peter Wright, about his work for MI5, was banned in England between 1985 and 1988, until the courts finally acknowledged that it's widespread availability in other countries made the ban meaningless.
On occasion the suggestion has been circulated that books should be 'rated' in the way films or computer games are, but I would never be in favour of such a move. I even have an instinctive dislike of labels that give a 'suitable' reading age range for a book. I think that once a child is an independent reader their choice of reading material should be up to them. I know that I have seen quite a few films/television programmes that I have regretted watching because of content that frightened or upset me, graphic images can be in your head before you realise they are happening, but I have not had such a reaction to any book. Books are different because of the part that your own imagination plays in your participation in the story. I think that people's fear of children reading something unsuitable is about protecting their perceived 'innocence'. It's as if life must be all 'everyone made it home safely for tea and buns' at the end like bloody Enid Blyton, and nothing bad ever really happens. I for one am really glad to see young people's fiction moving away from this and showing life in all it's rich variety, both positive and negative. Mind you, having said that, I do think J.K. copped out of killing off Harry which seemed to me to be the necessary finale of the series, she just couldn't resist the happy ending:-)