Definitely a work in progress, but it does quite a bit so far.  It's based off one I found online:

http://www.infinality.net/files/confluence-to-mediawiki-converter/

Source files:

http://www.infinality.net/files/confluence-to-mediawiki-converter/index.html

http://www.infinality.net/files/confluence-to-mediawiki-converter/convert.js

http://www.infinality.net/files/confluence-to-mediawiki-converter/convert.css

Original Sources:

http://projects.bsdpower.com/webtools/browser/phpbb/confluence2mediawiki-markup