This book, as the title implies, provides many excellent cover letters, however, it is poor in specifics. Unlike other books, this one contains very general advice and some statistics. I would recommend this book to those that want to get a sense of what other people's letters look like. I find that spending time dissecting these letter to be time consuming and tedious.
Books that I would recommend are:
"The Elements of Resume Style" by Scott Bennett and
"15 Minute Cover Letter" by Michael Farr and Louise Kursmark