The doc converter capability is this under utilized thing developers can leverage to transform a file of one type to another type. Out of the box you can convert a DOCX or InfoPath 2007 form to a Publishing page among a few other transformations including a powerful XML->HTML (via XSLT).
There is now a cool article on how to create PDF documents from DOC's already in a document library using the ASPOSE libraries. Granted, it's not a free thing, but still a good article showing the power.
BTW, there's a whole chapter on this subject in my upcoming book (Pro SharePoint 2007 WCM Development), specifically around creating a custom doc converter that takes the XML->HTML one to the next level complete with administrator and user settings interfaces.