Wordpress + Facebook Done Right: Load FBConnect asynchronously for XFBML and handle the channelUrl

gistfile1.php

/**
 * A class-based approach to bring in Facbook Connect asynchronously on every
 * frontend page load.  Also handles side-loading channelURL when using
 * Facebook's FB.init() method.
 * 
 * This fits nicely in any functions.php, or can be dropped in to a standalone
 * php file to use as a plugin.
 *
 * @link http://developers.facebook.com/docs/reference/javascript/FB.init/
 */
if( !class_exists('go_fbconnect') ) {
    class go_fbconnect {
        public function __construct() {
            add_filter('rewrite_rules_array', array($this,'fb_rewrite') );
            if( !is_admin() ) {
                add_action('wp_head', array($this,'add_fbconnect'), 15);
                add_action('wp_enqueue_scripts', array($this,'add_jquery'));
                add_filter('query_vars', array($this,'fb_queryvars') );
                add_filter('wp_headers', array($this,'output_channel') );
            }
        }

        /**
         * Be very sure we enqueue jQuery, as we need it in add_fbconnect()
         * 
         * Action: wp_enqueue_scripts
         */
        public function add_jquery() {
            wp_enqueue_script('jquery');
        }

        /**
         * Force asynchronous addition of the FB Connect javascript
         *
         * Action: wp_head
         */
        public function add_fbconnect() {
            $site_url = get_bloginfo('url');
    echo <<<FB
<script type="text/javascript">
(function() {
    jQuery(document).ready(function() {
        jQuery.getScript('http://connect.facebook.net/en_US/all.js#xfbml=1', function(){
            FB.init({
                xfbml: true,
                channelUrl: '{$site_url}/channel.html'
            });
        });
    });
}());
</script>
FB;
        }

        /**
         * Add a query var as a flag for channel.html
         *
         * Filter: query_vars
         */
        public function fb_queryvars($qvars) {
            $qvars[] = 'fb_channel';
            return $qvars;
        }

        /**
         * Add channel.html to our rewrites
         *
         * Filter: rewrite_rules_array
         */
        public function fb_rewrite($wprw = array()) {
            return array('channel.html.?$' => 'index.php?fb_channel=1') + $wprw;
        }

        /**
         * If WP has been called with our rewrite to /channel.html.?
         * simply output a permacached script inclusion and die.
         */
        public function output_channel($headers) {
            global $wp;
            if( !empty($wp->query_vars) and isset($wp->query_vars['fb_channel']) and $wp->query_vars['fb_channel'] ) {
                if(ini_get('zlib.output_compression'))
                    ini_set('zlib.output_compression', 'Off');

                @header('Expires: Wed, 1 Jan 2020 05:00:00 GMT');
                @header('Cache-Control: max-age=290304000,public');
                @header('Pragma: public');
                @header('Content-Type: text/html; charset=UTF-8');
                // Shouldn't be needed: '<script>document.domain = "mySite.com";</script>'
                die('<script src="http://connect.facebook.net/en_US/all.js"></script>');
            }
        }
    }
    $go_fbconnect = new go_fbconnect();
}