Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 12396)
+++ wp-includes/taxonomy.php	(working copy)
@@ -788,7 +788,7 @@
 	}
 
 	if ( empty($terms) ) {
-		wp_cache_add( $cache_key, array(), 'terms' );
+		wp_cache_add( $cache_key, array(), 'terms', 86400 ); # one day
 		$terms = apply_filters('get_terms', array(), $taxonomies, $args);
 		return $terms;
 	}
@@ -835,7 +835,7 @@
 		$terms = array_slice($terms, $offset, $number);
 	}
 
-	wp_cache_add( $cache_key, $terms, 'terms' );
+	wp_cache_add( $cache_key, $terms, 'terms', 86400 ); # one day
 
 	$terms = apply_filters('get_terms', $terms, $taxonomies, $args);
 	return $terms;