If you’re still using AOO (instead of switching to LibreOffice), you probably don’t need a book, but I’ve done one anyway. Taming Apache OpenOffice 4.1: Getting Started has been updated (from my book of the same name for v3.4) by me and members of the AOO Documentation Team, and reformatted and rebranded by me.
A free download of the PDF is available here.
Low-cost printed copies are available from Lulu.com.