In reply to christopher.

Yes, I use MarkdownPad for Windows. I write in it. Then, I use the Markdown On Save plugin to handle it on the WP side of things.

I've been tempted many times to move my personal blog over to a file-based blogging system that works with Markdown. But, I like the other stuff that WP offers too much to make the move. Writing long posts from the admin is one of the things I've never liked about WP. It's just never suited me.