Since I started a new project on behavioral targeting in online advertising, I decided to buy Linoff and Berry's book: Mining the Web (Transforming Customer Data into Customer Value).
The book starts by briefly explaining data mining with a marketing point of view. The next chapter describes the three different approaches to mining the web: mining structure, mining usage patterns and mining content. In my case, I was mostly interested by mining usage patterns, for example web logs. The following chapters are very general and give an overview of online retailing, digital content, advertising, customer value, customer tracking, etc. One good point of the book is that it contains several short industry case studies. Although not technical, they help understand how things work in big industrial projects.
To conclude, Mining the Web is an interesting introduction for people interested in applying data mining techniques to the web. Altough this book answers the "what" question, it doesn't answer the "how". Since it is a non-technical book, you will definitely need other resources for a deeper understanding of the field. The advantage is that the book is easy and pleasant to read from the beginning to the end. If you are interested by the field, you should also consult Jesus Mena's book: Data Mining Your Website (although a little older).