I have a website where people can discuss books of various topics, mostly technical and practical stuff. Lately I have noticed that some members are posting very, very detailed summaries/reviews of books. They are basically summarizing the whole book in so much detail that there's no point of buying the book anymore. I know summaries and reviews are of course not infringing content but should I be worried when it goes to this level?
I think proper question is that is there any law that prohibits rewriting and distributing core ideas from copyrighted material?