Ian has done some interesting work on converting word processing documents into a sustainable standard format; he chose DocBook, and considered the TEI(Text Encoding Initiative) format as well. These are both XML, both open, non-proprietary formats and both structured into sections, rather than being flat, like a word processing documents, or most HTML.
It struck me after hanging out with Ian for a couple of days that the ICE approach applies beyond the word processor / XML interface. ICE grew out of an idea for an interoperable word processing template that let Microsoft Word, OpenOffice.org Writer and XHTML interoperate via the use of templates and style. Not a magic converter that would attempt to map any-old Word document to any-old HTML document to any-old Writer document but a way of working in any one of those systems, using styles and sensible conventions that give you documents that can be interchanged with the others.
Ian's success with mapping ICE word processing documents to a 'slice' of DocBook show that the ICE approach is really suited to general-purpose interchange. Maybe it shouldn't be called the Integrated Content Environment, but Interchangeable Content Environment.
ICE is ready for brave, resourceful people to try. At the moment it is quite good at making courseware from OpenOffice.org and Microsoft Word documents, and on the RUBRIC project we're training it to do project document management as well. If you want help getting started with ICE please contact me.