<?php
/**
 * clean curly quotes and other bad characters
 */
function clean_characters($post_id) {
	$post_id = (int) $post_id;
	if (!$post_id)
		return;
	global $wpdb;

	$wpdb->query('UPDATE wp_posts SET
		post_content = REPLACE(post_content, "’", "\'")
		WHERE ID = ' . $post_id);
}
add_action( 'save_post', 'clean_characters', 1000 );
?>