As you may know, I use Word (evil, evil Word) to lay out the paper editions of my books, because proper layout software is really expensive. Today, Passive Voice has a post about using OpenOffice, and he mentions that he also uses Word, and then down in the comments (always read those!) people talk about tricks to use with Word as well as something called LibreOffice, which is like OpenOffice but allegedly better. I use neither OpenOffice nor LibreOffice, so I can't judge the worth of those tips, but they may help you. I also don't know if the Word tips will help me, since my version of Word is a decade old, but I'm definitely going to give them a shot.
One thing that gets mentioned is the value of templates. I have to agree that templates (whatever kind works for you) are awesome. Laying out Trust went so much quicker this time because I essentially had a template (i.e. the Trang layout with a few tweaks), so I just replaced the text and changed chapter and page numbers. In the past I've been a little dumb about it and opened up brand-new files for each chapter, which meant I had to input and format the headers, format the chapter numbers, etc., etc. It cuts the amount of time you spend laying things out probably by at least a third if you just save the last chapter under a new name and use it as a template.