Modification of Habari's Google Analytics plugin to allow for caching the tracking file locally. Should also validate as real XHTML.

googleanalytics.plugin.php

<?php
class GoogleAnalytics extends Plugin {
    function info()
    {
        return array(
            'url' => 'http://iamgraham.net/plugins',
            'name' => 'GoogleAnalytics',
            'description'   => 'Automatically adds Google Analytics code to the bottom of your webpage.',
            'license' => 'Apache License 2.0',
            'author' => 'Graham Christensen',
            'authorurl' => 'http://iamgraham.net/',
            'version' => '0.5.1'
        );
    }

    public function filter_plugin_config($actions, $plugin_id)
    {
        if ($plugin_id == $this->plugin_id()) {
            $actions[]= _t('Configure');
        }
        return $actions;
    }

    public function action_plugin_ui($plugin_id, $action)
    {
        if ( $plugin_id == $this->plugin_id() ) {
            switch ($action) {
                case _t('Configure'):
                    $form = new FormUI(strtolower(get_class($this)));
                    $form->append('text', 'clientcode', 'googleanalytics__clientcode', _t('Analytics Client Code'));
                    $form->append('checkbox', 'loggedintoo', 'googleanalytics__loggedintoo', _t('Track logged-in users too'));
                    $form->append('checkbox', 'cache', 'googleanalytics__cache', _t('Cache tracking code file locally'));
                    $form->append('submit', 'save', 'Save');
                    $form->out();
                break;
            }
        }
    }

    /**
     * Add update beacon support
     **/
    public function action_update_check()
    {
         Update::add( 'GoogleAnalytics', '7e57a660-3bd1-11dd-ae16-0800200c9a66', $this->info->version );
    }

    public function filter_rewrite_rules($db_rules)
    {
        $db_rules[] = RewriteRule::create_url_rule('"ga.js"', 'GoogleAnalytics', 'retrieve_cache');
        return $db_rules;
    }

    public function act($action)
    {
        switch ($action)
        {
            case 'retrieve_cache':
                self::retrieve_cache();
                break;
        }
    }

    public function retrieve_cache()
    {
        if (Cache::has('ga.js')) {
            $js = Cache::get('ga.js');
        } else {
            $js = RemoteRequest::get_contents('http://www.google-analytics.com/ga.js');
            Cache::set('ga.js', $js, 86400); // cache for 1 day
        }

        // Clean the output buffer, so we can output from the header/scratch
        header( 'Content-Type: application/javascript' );
        echo $js;
    }

    private function detect_ssl()
    {
        if ($_SERVER['HTTPS'] == 'on' || $_SERVER['HTTPS'] == 1 || $_SERVER['SERVER_PORT'] == 443) {
            return true;
        }

        return false;
    }

    function theme_footer()
    {

        if ( URL::get_matched_rule()->entire_match == 'user/login' ) {
            // Login page; don't dipslay
            return;
        }

        $clientcode = Options::get('googleanalytics__clientcode');

        if ( Options::get('googleanalytics__cache') ) {
            $ga_url = URL::get() . 'ga.js';
        } else {
            $ga_url = (self::detect_ssl()) ? 'https://ssl.google-analytics.com/ga.js' : 'http://www.google-analytics.com/ga.js';
        }

        // always output the first part, so things like the site overlay work for logged in users
        echo <<<SCRIPT1
<script src="{$ga_url}" type="text/javascript"></script>
SCRIPT1;

        echo <<<SCRIPT2
<script type="text/javascript">
//<![CDATA[
try {
var pageTracker = _gat._getTracker("{$clientcode}");
SCRIPT2;

        // only actually track the page if we're not logged in, or we're told to always track
        if ( User::identify()->loggedin == false || Options::get('googleanalytics__loggedintoo') ) {
            echo <<<SCRIPT3
pageTracker._trackPageview();
SCRIPT3;
        }

        echo <<<SCRIPT4
} catch(err) {}
//]]>
</script>
SCRIPT4;

    }

}
?>