Weirdly for a book of this nature, it is an ideal toilet book. Each page contains a message. Indeed, you shouldn't read the whole book in one sitting, or plane ride. Instead, read it a few pages at a time, then digest that. Repeat and learn.
And what will you learn? Well, obvious stuff really. But the best tips are always those that have been staring you in the face. Most people don't like clutter. The best way to design a site is to see how people use it. That sort of stuff.
Now, I don't necessarily agree with everything in this book. It is written purely from the perspective of the designer. A successful designer working big ticket contracts doesn't need to worry about the likes of SEO for instance. But the rest of us do. Its one thing adopting a less is more approach to the prose on your site, but if nobody can find the damn thing its irrelevent. Plus, I don't think there is anything wrong with the way Amazon lets you save items (read the book to find out what I'm going on about here).
However, there is an awful lot of stuff in this book that I do agree with, and still more stuff that I hadn't really considered. And best of all, the author's ideas are backed up with clear examples. I particularly liked the example of the Paris Underground Route Finder. Such an obvious fault to anybody who uses the thing, yet so easy to overlook if you are just designing from an idea.
Design is only part of my job. I spend more time coding and doing other web-related tasks. Normally I hate books purely on design, because, well, they are purely on design. However, this one I liked because it wasn't completely up its own posterior, and it delivered its message in an easily digestible format. If, like me, you hail from the Developer side of the coin, then this book coupled with "Don't Make Me Think" are the two design related books I would consider essential.