It would be useful to be able to edit (and copy/paste) content using markdown format.
This extension seems to offer that: http://www.mediawiki.org/wiki/Extension:MarkdownSyntax
I personally don't see where this would come in handy unless we started to use markdown as the primary syntax. This would just add one more way to do content which would just add to confusion on markup.
I will bring it up in the Mailing List though and see what others think of the idea.
Looks pretty quickly decided in the Mailing List by others that we shouldn't allow multiple syntaxes. We will continue to stick with MediaWiki syntax for simplicity and sanity's sake.
There is some work being done to a plugin for the Q&A system to use markdown as a code syntax there to allow for some formatting.
Janet Swisher pointed out in the Mailing List that you can use Pandoc  to convert between markup syntaxes. So you can code in markdown and use this to convert before importing into WPD.
Discussion is resuming on this from the Telcon.
Just a quick thought from the telcon from Paul:
Using Markdown should probably by done client side, but information posted to the server should remain in true MediaWiki syntax.
(If I heard properly that was the gist of it.)
Paul (Irish) and I talked about the markdown stuff today at the Docsprint. We are pretty sure using Pandoc to do the conversion on the server is the way to go. The thing is we need to have it configured to interpret in between the save of a page using a template and as the content is being written to the DB. I'm not sure exactly where it needs to fall but that sounds right to me. (Actually, just thinking about it in more detail I need to email Alex to see how the form system works exactly when saving data to figure out the best method.)