I already do all my work in markdown. I got into the habit because of github, and haven't turned back since. The "killer feature" was that my documents work absolutely everywhere, and can easily be converted to a Word, PDF or HTML document on a whim. Leave the format "prettiness" to style sheets where it belongs. The side effect is that it clobbers the multiple-styles problem many corporate documents amass after more than a few people have edited them. The number of documents I've worked with that had UK, Canadian and US English all embedded in a paragraph-by-paragraph manner over the years...

Mind you, I started out in that frame of mind, since at the end of the 80's I used to write all my documents in a format that I no longer remember the name of. What I do remember is that it used dot codes, so something italicized would start with .i and .u for underlining. The purpose was to allow the dot matrix printers to over-strike, which provided much higher print resolution than the printer would normally be capable of. It had higher level codes for things like titles, etc, which is the connection I make to markdown.

Markdown languages allow you to get things looking reasonably good with extremely few attention-diverting things like format getting in the way of progress.