The LibreOffice Documentation Team has published two books: the LibreOffice 4.0 Math Guide and the LibreOffice 4.0 Base Handbook.
Free PDFs can be downloaded from The Document Foundation’s wiki.
Printed copies can be purchased here. (Published by Friends of OpenDocument Inc.)
Note: The Base 4.0 Handbook is identical to the Base 3.6 Handbook, except for the cover, the ISBN, and the title and copyright pages. If you have the earlier version, you don’t need this one. The Math 4.0 Guide has new and revised material in it.