NB - The module has now been extensively developed and both Drupal 6 and Drupal 7 versions are available. The module is at:
This module is designed to be part of a whole dev/staging/live deployment process.
Basically, you can push development changes up to a beta copy of a new site - and then using the Data Export Import module you can export data from a live site and then import that data into the beta site to produce a new version of the site.
BTW - The best way to test is to install on a Drupal site - export data to a file - then alter the existing data - then re-import the data file. This will reset the data back to what it was when it was exported. There are checks in place to make sure that when importing the data the vocabularies and content types match etc - this is to prevent data being imported into Drupal site which don't have the correctly matching vocabularies/content types etc.
Later I may be able to add a profile to export/import vocabularies which can be used before exporting/importing the vocabulary terms.
Thanks for any help with testing and reviewing.