Personally I'm currently writing almost everything (article-lenght stuff and posts for my website, mostly) in reStructuredText and then using one of the many tools available to transform it.
The best results for PDF generation are still those that go through LaTeX, and they may require some knowdlege of it for customisation (which works for me, since I come from that :) ), but people who don't know LaTeX can still ask somebody else for that bit of customisation and concentrate on writing the text.
There are of course also tool to generate HTML and ePub, and also a ODT, which would then allow to generate .doc files for submission to traditional publishers.
Most of those tools are written in python (a good number comes straight from docutils) and of course they don't have dependencies on proprietary software.
I've been looking also for a toolchain based on pandoc, which is able to generate even more formats, but it's support for reStructuredText is still somewhat limited. On the other hand it is an alternative for people who would like to use markdown (it's "native" source format), and of course it is still totally free.