• http://michaelosmith.com/node/10 Removing Unused Taxonomy Terms (DELETE FROM term_data USING term_data LEFT JOIN term_node ON term_data.tid = term_node.tid WHERE term_node.tid IS NULL AND term_data.vid = vocabulary_id_# ... # = Vocabulary) mittels http://drupal.org/project/sqlcron (cron sql)
• nicht verwendete Taxonomy Tags entfernen: http://agaric.com/note/delete-unused-taxonomy-terms-from-free-tagging-vo...
• http://groups.drupal.org/node/16979 ... SQL-Schnipsel
• http://drupal.org/project/views_bulk_operations - If you can set up a view showing all orphaned terms it should be a breeze to get Views Bulk Operations to delete them.

Module

• cleantaxonomy
• delete_orphaned_terms