Today I'm in basicthinkingblog.de an article on the WP super cache plugin read. In the comments, the discussion went on, which I found very inspiring (because I'm very much the theme of "burden" on Web servers of interest). There, I found also a nice 3-liner to a logged-in users at the foot of the website, the Number of requests to the server and the duration the line you wish to 

  <Php if (is_user_logged_in ()) {?>
 <? Php get_num_queries ();> Requests
 at <timer_stop php (1);?> sec. <php}?>