I used asciidoc to write a book with Manning, and what I have to say is that I'm personally not a fan. The main reason is the tooling in ruby. Maybe if asciidoc was more popular than it would have more implementations in more languages, but it's really tedious to work with it in the current situation IMO.

The other thing is that, it was not easy to work with LaTeX in asciidoc last time I was doing it.

Smaller issues: the syntax really sucks.