gistfile1.aw

<?php
/**
 * Add description to menu
 * @author Bill Erickson
 * @link http://www.billerickson.net/code/add-description-to-menu
 *
 * @param string $item_output 
 * @param object $item
 * @return string modified item output
 */
function be_add_description( $item_output, $item ) {
	$description = $item->post_content;
	if (' ' !== $description ) 
		return preg_replace(  '/(<a.*?>[^<]*?)</', '$1' . '<span>' . $description . '</span><',  $item_output);
	else
		return $item_output;
}
add_filter( 'walker_nav_menu_start_el', 'be_add_description', 10, 2 );