Let me start by quoting the first paragraph from the back cover:
Despite the astronomical number of hours invested in developing websites for commercial and other uses, it is now clear that many websites are poorly designed and have floundered as a result.
This book focuses on the need for usability. However good the content, the navigation and the aesthetics the site will likely fail to meet expectations if it is not usable.
Patterns in software design terms refer to the encapsulation of standard solutions to common problems. Actually I should qualify the use of 'standard' with 'effective'. A standard solution may be ineffective. We see a great deal of that when surfing the web, where so many sites seem incapable of understanding that the effective visual aspects of printed fliers do not transfer to effective electronic 'fliers'. In both cases we have a minute window of opportunity to grab the attention of an individual. Beautiful and/or startling graphics may achieve that on paper but if they result in loading times in excess of a few seconds then they will be failures on the web.
In this book the author covers 79 patterns (and their inter-relationships) that cover issues of web usability. The book derives from a workshop at OT2001 (held in Oxford, England). Those that are familiar with this event will realise that this book will be a serious and well-designed example of a pattern language. Indeed I think the book actually is a good case study of the concept of a pattern language and is worth studying from that perspective. However if you are responsible for a website (if only your own home page) this book could be a major factor in helping you do a professional job rather than the job that so many so-called professionals are satisfied with.