Free PDFs can be downloaded from the wiki. Printed copies can be purchased here.
Sep 10 2012
May 10 2012
The LibreOffice Documentation team has published another book: the LibreOffice 3.4 Draw Guide. Individual chapters and the full book are available on the wiki. A printed copy can be purchased here. Other books for v3.4 (Impress Guide, Calc Guide, Math Guide) in various stages of completion are also on that wiki page.