I started it when I was writing lots of text on an Alphasmart stand-alone keyboard, almost the best tool for first-draft writing. But really bad for editing. So I'd upload raw text to a file, for further processing on a real conputer. I wrote a program to do preliminary cleanup, making it more like HTML. Emacs after that.
Yes, that was over a decade ago. The program is written in Modula 3.
I discovered that the notation I was using on the alphasmart was more convenient than raw HTML, so I continued to use the ad-hoc notation even after I migrated to a laptop, and slowly changed it and the program according to taste. The program now generates .fodt files, which I do not edit.
My notation has no log-term syntactic nesting constraints (as HTML does with its and tags) so it is a natural for use in a revision management system. (Merges preserving tree structure are notoriously hard to do correctly; i.e., yielding valid tree structure after).
I'm considering changing to markdown. A project I'm involved i has chosen Asciidoc instead.
I consider ease of use with a revision management system (I use monotone) to be crucial.
The main feature I've found to make this easy is for the markup to use separators instead of brackets whenever possible. Thus use a mark to separate paragraphs rather than two to enclose them. Maybe there are a few things that can't be anaged this way, but for the most part the big things can be.
-- hendrik