The Modern Web touches everything I could possibly think of regarding web design and development. It helps you understand technologies and best practices for:
Obviously the book is just a snapshot and technology and techniques continue to evolve after publication. However, if you are a bit behind on what's happening or need to continually stay informed of technology for web design and development, The Modern Web will save you a lot of hours getting up-to-speed.
The Modern Web organizes the information quite nicely, clearly explains the importance, and provides code snippets and samples at just the right level to demonstrate it's use. If you aren't really interested in understanding implementation, The Modern Web is a great overview. The snippets and code samples are there to support the written content and do not get in the way of the information. You can easily read though the material and skip any code and snippets and learn a lot. If you are a web developer, designer, or more of a visual learner like myself, the samples are just right to digest the information and walk away with good knowledge of implementation. If you want to take the information further, there is a list of resources for Further Reading at the end of each chapter should you wish to dive even deeper.