gistfile1.js

<script type="text/javascript"> 
//<![CDATA[ 
var get_disqus_num_replies = function() { 
        var links = document.getElementsByTagName('a'); 
        var query = '?'; 
        for(var i = 0; i < links.length; i++) { 
                if(links[i].href.indexOf('#disqus_thread') >= 0) { 
                        query += 'url' + i + '=' + encodeURIComponent(links[i].href) + '&'; 
                } 
        }
        var s = document.createElement('script');
        s.type='text/javascript';
        s.src = 'http://marcador.disqus.com/get_num_replies.js' + query;
        var body = document.getElementsByTagName('body')[0];
        body.appendChild(s);
};
get_disqus_num_replies();
//]]> 
</script> 

Why not just calls:

DISQUSWIDGETS.getCount();

or count on server side using:

https://github.com/disqus/DISQUS-API-Recipes/blob/master/php/get-thread-details.php

@vinarkrsharma: thanks, works great!