Auto-Tagging with Author Username

gistfile1.aw

<?php

function wpized_tag_post_with_author_username($post_id) {
	if($parent = wp_is_post_revision($post_id)) {
		$post_id = $parent;
	}
	$post = get_post($post_id);
	if($post->post_type != 'post') {
		return;
	}
	$user = new WP_User($post->post_author);
	if(!in_array('administrator', $user->roles)) {
		wp_set_post_terms($post_id, $user->user_login, 'post_tag', true);
	}
}
add_action('save_post', 'wpized_tag_post_with_author_username');

?>

Might want to do if( !in_array('administrator', $user->roles) ) just in case they have more than one role, which I've never seen, but still :-)