This is a remarkable book. First of all, it is beautiful: beautifully typeset and laid out in a beautiful format on beautiful paper. Prof. Bringhurst's love of his subject, clearly witnessed by the level of detail of his exposition, makes this book a delight to read both as a narrative, binding together the historic and modern arts of typography and booksetting, and as a reference source from well before mutton to well after pilcrow.
Why, then, do I say it is dangerous? Simply this: I makes me completely dissatisfied with every piece of electronic publishing I have ever done. Books, manuals, papers, letters, business cards: all mediocre scratchings.
Prof. Bringhurst is, in this book, a master of the art of damnation through faint praise. His analysis of the broken kerning of Times New Roman, while quite reserved and polite, show by clear example just how badly broken it is -- it needs no other condemnation -- and should make all those users of MS Word's default font family squirm at their keyboards.
Notable, too, by their complete absence, are a number of font families that many of us take for granted, but I won't name them here, except for Comic Sans. The author is not writing for web users, though he does mention, briefly and adequately, the problems of showing a decent text on a computer screen. I suspect his silence is to draw a veil over what for him must be some of the most depressing items of typographic experience.
Finally, this book is not for everyone. It needs a little persistence to read; and you will need a degree of curiosity about at least one aspect of fonts and typesetting to enjoy it. But given these pre-requisites, enjoyment is guaranteed.