Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 12609)
+++ wp-includes/taxonomy.php	(working copy)
@@ -195,6 +195,39 @@
 }
 
 /**
+ * Reverse the effects of register_taxonomy()
+ *
+ * @package WordPress
+ * @subpackage Taxonomy
+ * @since 3.0
+ * @uses $wp_taxonomies Modifies taxonomy object
+ *
+ * @param string $taxonomy Name of taxonomy object
+ * @param array|string $object_type Name of the object type
+ * @return bool True if successful, false if not
+ */
+function unregister_taxonomy( $taxonomy, $object_type = '') {
+	global $wp_taxonomies;
+
+	if ( !isset($wp_taxonomies[$taxonomy]) )
+		return false;
+
+	if ( !empty( $object_type ) ) {
+		$i = array_search($object_type, $wp_taxonomies[$taxonomy]->object_type);
+
+		if ( false !== $i )
+			unset($wp_taxonomies[$taxonomy]->object_type[$i]);
+
+		if ( empty($wp_taxonomies[$taxonomy]->object_type) )
+			unset($wp_taxonomies[$taxonomy]);
+	} else {
+		unset($wp_taxonomies[$taxonomy]);
+	}
+	
+	return true;
+}
+
+/**
  * Add an already registered taxonomy to an object type.
  *
  * @package WordPress