I never found that book useful because the scenarios were too pat and unhelpful for someone in my situation (and, I suspect, most writers'). They'd talk about a highly successful cardiologist, member of three different professional associations (and president of one), who was writing a diet book. As if someone like that were a common case, applicable to everyone reading the book and a really, really difficult sell, but you know, that's what being a savvy agent's all about.
I'm with the others on this. Borrow from the library, go on-line. In my experience, on-line sources like AgentQuery are more accurate and up-to-date than the books, but it never hurts to compare sources . . . which seem never to agree.