I just found a little easter egg to create diffs of OpenOffice.org documents (*.odt) on the command-line.
All you need to have the following two new tools:
- odt2txt for extracting the content of an OpenOffice.org document. (A Debian package is available)
- oodiff for comparing the content.
The real easter egg is that you can compare your local copy with the latest subversion revision. Well, oodiff does not really connect to subversion, but uses a local copy of the .svn directory. Git and Mercurial are also supported.