Hopefully this is correct place to report this
SO is really sluggish tonight, looking into it a little more there have been many times that I was waiting for nearly 20seconds for the ads to display - see screen shot below from firebug. The add that displayed was for server fault if it makes any difference.
As far as page rendering is concerned, I had clicked on the questions tab, the page rendered as far as the bottom of the questions and then stops waiting for the ads. The paging controls and footer do not appear until after the ads have finally rendered.