The Drupal 6 version of @font-your-face is mostly in maintenance mode now. New features added to the Drupal 7 version will not be back-ported by the maintainers, though patches submitted by others will be reviewed and committed. As a result, much of the main documentation for @font-your-face only applies to the Drupal 7 version. Specific differences should be documented here.

The user interface is located at: admin/build/themes/fontyourface