The purpose of this book is to increase your conversion rate, in other words sales on your site using a multitude of different methods. It tries to cover all bases everything from usability issues, writing effective persuasive copy, web analytics, understanding your customers etc. It bashes on about the what's and the why's but often avoids the how's (especially on web analytics) which lets the book down.
If you're new to all this and want an overview then this might be the book you're looking for, the reason I say might is that the book is so repetitive that it could easily have been a third of the size and would still have covered everything it did, this is rather annoying as they could have spent more time digging deeper into topics than just fleeting over them and it made me feel a little cheated.
Don't get me wrong though, there is a lot of good stuff in here but it still falls short of an in depth study (which it promised to be) and does feel a little disjointed; it's a shame they wasted so many pages repeating themselves.
Oh and one last think you should be aware of would be acronym overload. These boys love their acronyms!