This book is very simpilar to The Missing Manual: Mac OSX Leopard Edition - much of the directly Mac related content is exactly the same in both books. However, it's not just a cover change and a few paragraphs artufully inserted: there is Windows switching information available here that is NOT in the other book.
I think David and O'Reilly would have been smarter to set out to make this two really separate books from the start. Certainly both these books are too big: if you stripped all the Windows stuff out of the first and stripped all the basic "this is how a Mac works" stuff out of this, you'd have two volumes of more reasonable size. However, that's not what they did, so there is a lot of duplication. If you are just a Mac user, you need the other book, not this. If you are a recent switcher, this is the book you want.. though you may want the other also as this does not have everything that has..
This is the book I will give my wife once her XP PC finally dies - I have high hopes for that: it's been shutting off unexpectedly and making grinding noises now and then. The minute it does, I'm buying her a Mac and handing her this book.. that will be a happy day indeed.
She'll enjoy the book, too. David writes well, keeps it interesting and amusing, and knows how to explain semi-technical subjects well.