While working on my own book for Apress, Free Software for Creative People, I've also been typesetting a 240 page poetry book by Richard McKane using Scribus, for the publisher Hearing Eye. Years ago I used to use Quark Xpress for this sort of project, so I was pleased to find out that free software can now do the same job.
A great deal of the web is GNU/Linux based: most of it runs on LAMP servers, and some content is created with great tools such as the GIMP, Inkscape and a fancy notepad (or Vi, or Emacs—don’t start). Pen tablets are recognised and used, you have access to effects plug-ins, you can work on bitmaps or vectors (thanks Mr Pierre Bézier! Your name will remain in history). On the other hand, as soon as you want to have your work printed, it’s another matter.