I've been on a quest for a long time to figure out the best way to write and publish documents. It has been a quest that has taken me years but I finally have a system that I am extremely happy with.
What I wanted was to be able to write via Emacs (my editor of choice) and output to anything else. Want my document in HTML? You can have it that way. Want a PDF? Yes, I can. What is in Word? Though I can't stand the application, and I don't actually own it, yes I would like to be able to output Word docs without actually opening another application. Just writing it in Emacs, run a process on it, and the I have a Word document!
This has been nothing but a pipedream for a long time. At the beginning I tried to use this idea with [LaTeX], and I could get the PDF output to look outstanding. The HTML output took a lot of work to get right, and I never got [latex2rtf] working well enough that I could send that document anywhere else. So I had to figure out what else to use.
Then I started playing with [Markdown]. I really liked the easy format, but it really only would output into HTML. With a bit of work, I could do a PDF (html2pdf or something like that ), but something to load up with Word? Forget it! And even the PDF looked kinda bad. The same thing with Textile and reStructuredText -- HTML and that was about it. I did prefer the Markdown format over LaTeX based on it's simplicity but I still haven't found my Holy Grail yet.
Just a few months ago I somehow stumbled on [Pandoc]. I think it was on Google+, on someone's random post. I was floored when I read it: "Take a file in format X, run Pandoc on it, and get format Y, with varying degrees with X and Y?" This seemed like just what I was looking for!
But did it work as advertise? Yes it did! It understands everything about Markdown that I currently throw at it. To get the PDF conversation script working, it used LaTeX as an intermediarty so you have to have LaTeX installed. But Word? Not directly -- but it does have RTF support, which is even better (since it's more portable). It also does [ODT] format, which means I can open up in LibreOffice and tweak for presentation if need be. The ODF output is better than the RTF output, in my humble opinion.
The biggest surprise I got was that it does conversions to [S5] -- so I can do representations in Emacs/Markdown and be able to present with just a browser. I have done this and it works amazingly well.
One thing I haven't tried yet is that is also outputs to ePub. If it only did the closed Mobi format for my Kindle.
So, yes, if you are looking for a "write-once, publish to anything" scheme, you can't do any better than [Pandoc]