Here's my suggestion. If you treat D3 as the author intended, the whole enter/foo/exit thing, you're doing well. If you start in and treat it as jQuery, you're not doing a service. I promise to check out your book as I really love MEAP from manning (and I buy them frequently).
I truly wish you the best. Authoring a book is a tough job.
Well, I can guarantee it's not going to be like jQuery, since I'm really not all that familiar with it. The book does deal with the structure of D3 in detail, which you'll see in the chapters that are already up on the MEAP, and then it gets into specifics for creating charts, using layouts, custom events, maps and so on.
And you're right, for those of you thinking of writing one of these books, it is a hell of a time commitment and, on top of that, you have to know something pretty well to be able to make it, but you have to know something inside and out to be able to explain it.
I truly wish you the best. Authoring a book is a tough job.