One thing needs to be clear before you buy this book: it is a dictionary, not a book of grammatical rules. That is, it is much more of a descriptive work than a prescriptive one. A lot of the reviewers here seem to take that to mean that it advocates some sort of linguistic anarchy, but what it really does is inform readers about the different aspects of various usage issues so that they can make an informed decision instead of blindly obeying the strictures in books like The Elements of Style. Everyone serious about the English language should own a copy.