Some of you interested in document design open source tools might want to check out NewsForge's Designing a book with LyX. From LyX's About page:

LyX is an advanced open source document processor running on many Unix and some non-Unix platforms. It is called a "document processor", because unlike standard word processors, LyX encourages an approach to writing based on the structure of your documents, not their appearance. LyX lets you concentrate on writing, leaving details of visual layout to the software. LyX automates formatting according to predefined rule sets, yielding consistency throughout even the most complex documents. LyX produces high quality, professional output -- using LaTeX, an open source, industrial strength typesetting engine, in the background.

LyX has also been ported to Windows and Mac.