I came across this book about Google Wave. Its an ongoing and ever upgrading book about what Wave’s all about and goes in detail about how to learn and become a better wave surfer (:D). Gina has decided that she is going to keep updating that book as Wave progresses and grows. Check it out:
The Complete Guide to Google Wave: How to Use Google Wave
"Google Wave is a new web-based collaboration tool that’s notoriously difficult to understand. This guide will help. Here you’ll learn how to use Google Wave to get things done with your group. Because Wave is such a new product that’s evolving quickly, this guidebook is a work in progress that will update in concert with Wave as it grows and changes. Read more about The Complete Guide to Google Wave, and follow us on Twitter for updates and Wave tips. "
They also, now, have a pdf version of the book (link on their site), to download and use offline.