[Aloha]

I edit a webpage, its a modern page with php, JSON and jquery elements - but the large majority of it is in html, markdown does nothing for me, because I'd need to convert it anyhow back to HTML for the webserver.

Markdown however would be very useful in replacing the groff code used in man files for example, if perhaps it were a little more expressive - it has the advantage of being easy to parse when not render, and easy to build a renderer for.