I\'ve heard discussion about how OpenOffice (ODF) files are compressed zip files of XML and other data. So making a tiny change to the file can potentially totally change th
If you don't need the storage savings, but just want to be able to diff OpenOffice.org files stored in your version control system, you can use the instructions on the oodiff page, which tells how to make oodiff the default diff for OpenDocument formats under git and mercurial. (It also mentions SVN, but it's been so long since I used SVN regularly I'm not sure if those are instructions or limitations.)
(I found this using Mirko Friedenhagen's page (cited by Craig McQueen above))