A new Wave Manual written by LifeHacker founder Gina Trapani along with LifeHacker editor Adam Pash has been released - online free to read. The Complete Guide to Google Wave was announced this week on This Week in Google - one of Leo Laporte's live TWIT.tv Podcasts.
Trapani stated she managed the production of the whole book entirely in Google Wave, and noted she ran into a few minor problems (like inviting the wrong people to a wave etc). Trapani also mentioned she would have loved to author the whole book in Wave, but didn't feel Wave was up to the challenge yet, since it is still in development and has a few flaws before it would be up to that challenge.

Trapani mentions that the book is released under a Creative Commons Share-alike attribution etc. license and that the book is currently available on the web only, as a mediawiki site. The book will be open to public collaboration/suggestions/feedback etc. and will be available in PDF in the near future.
From the site:

In case you missed the link, check it out here.