I just ran across this link today and was wondering if anyone else had checked it out: http://shudson310.blogspot.com/2006/05/docbook-xsl-170-released.html

It looks like there is a docbook project up on sourceforge that has XSLT support for going from WordprocessingML into DocBook (or the other way around). I haven't had a chance to look into it yet... sounds pretty cool though.