Fantastic! I'll go grab the Blogsmith bundle right away. As it is I write in TextMate and copy/paste the resulting pseudo HTML into the browser field. I can see my Sunday afternoon slipping away...
The Safari plugin also sounds very handy, although I try not to write directly into browser text fields. Wordpress oddities and browser crashes can lose whole articles. I'm sure the same things has happened to you at TUAW.
We use Wordpress at Wired.com, but obviously I can't add plugins to the back end (I'm a writer, not admin). Do you have a version for Textmate? A plugin perhaps? If the answer is yes, I will love you forever.
Well, truth is, most of the functionality sprouted from my desire to have TextMate's default functionality in the admin TextArea. If you haven't checked out the Blogsmith Bundle, I think you'll find it's exactly what you're looking for, though. Autocompletion, link detection, all that good stuff. It's a huge bundle and the documentation is a little scattered. I'm working on a video demo site for it, too.
The bundle was built specifically for Blogsmith users (TUAW, Engadget, etc.), but there are really only two parts of it which are specific to that platform (Autofill and Image upload). Both of those features are only necessary because Blogsmith doesn't have XMLRPC features like WordPress does. So if you combine the Markdown parts of the Blogsmith Bundle with the default TextMate blogging bundle, you're set. Forever.
Also, I'm working on a version of this plugin as a Safari extension to take over any text field, so you could use it in Wired's admin panel without disturbing anyone else's install, and it would render the HTML right in place. I'll keep you posted.