Very nice plugin. Here are some things I'd like to see in future versions if possible:
1. The ability to switch between the MD toolbar and the traditional HTML editor. Sometimes one needs a little more control over the content and it is nice to get into the HTML. Especially since the conversion from HTML back to MD is somewhat shaky at best.
2. The ability to have MD features installed on a per-user basis. Not everyone knows MD.
3. The ability to batch-convert old posts that were made using a previous MD editor to HTML. (This maybe should be a separate plugin?)