I'm currently setting them up with Sublime Edit, but it's not quite ideal as it's overly complex for what they need and I still have to manually configure it to default to UTF-8.
Many people care more about rendered markdown than about raw markdown, and would prefer to edit closer to the rendered result than to the human readable but not what they're interested in text. For those people, this eliminates the "write - render - check" cycle.
If there was an equivalent of ckeditor or tinymce that could output markdown or textile instead of html, I'd find that extremely useful.