WordNet, the book, is a must to anyone who wants to use or learn about WordNet the semantic network/lexicon. The early chapeters of the book discuss the strategies and treatment of the various parts-of-speech by the development project. The later chapters are contributions of researchers that have applied the database to various investigations.
WordNet, the database. is free for non-commercial purposes and comes with a simple viewer and software that can be adapted to your own use. As such, it is (in my opinion) the finest free lexocographic resource available.
You shouldn't think about buying the book until you have played with the database. But if you do and want to know more about its development and uses (and you don't feel like finding libraries with 10 year old obscure journal articles), this book is for you.