Oh, I hadn't considered posting that there, but since my ultimate aspiration is to end up fandom_wank, I should probably do that! ;)

I agree that the book violates Salinger's copyright. The issue really is whether the author has a fair use affirmative defense (and I don't really think he does, but I can't be certain until the order comes down from the court, lol!)

Also, you're right about Harry Potter. While it may use some elements that are common to Tolkien and the fantasy genre in general, there are sufficient differences between the book that there is essentially no infringement. I just brought that up to show that, IMO, the "trading on popularity" argument is a bit weak.