An excellent introduction to the concept of Universal Design which demonstrates both how to apply the principles throughout the design through implementation process and clearly demonstrates that accessibility is just one aspect of universal design.
A couple of early comments in this book make it really obvious what the book is about. One of these asks which is to blame for someone who can't walk being unable to get into a building - their wheelchair or the steps in front of the building. The second points out that there is no us and them with regard to accessibility and gives the example of someone using a mobile phone to access the web whose fingers are too big to properly click on the links. These two examples clearly demonstrate the importance of the material in the book to ALL web sites.
The main content of the book covers a whole range of different design considerations from meta data, forms, tables, video, audio, scripting, Flex, Flash, and Silverlight. In each case a few examples of specific problems with that particular technology are mentioned as well as some specific information on solutions to those problems. The size of the book means that each section is only briefly covered with mention of the most obvious of the problems and the book isn't a complete answer to all the problems you might be confronted with in any particular area. It does set you on the correct path though so that you know at least in general what sort of solution you should be looking for. The book advocates progressive enhancement so as to ensure that pages are still usable by those who do not have all of the more advanced technology.
The other theme running through the book is how important it is that universal design principles should be considered from the beginning of the design process and not left to be tacked on at the last minute just before implementation. The reasons for this are made very clear in the book.