Good news from Slackbook authors. They are working on a major release: 3.0. This version is a complete re-write and should use the latest Slackware (probably 12.1) as the base. This version is predicted to come out in Mid 2009, but we will never know. I hope it's synced with the release of Slackware 12.2 in 2009.
The new book is being written with vi in Docbook format. Complete instructions for building HTML and pdf versions of the book will also be provided at the site, along with any extra Slackware packages (and source code of course!) if any special tools not included in current versions of Slackware aren't included in Slackware.