If you have ever used pop unders then you have probably benefited from longer time on page statistics and also pages viewed per visit.  But what happens if you remove the pop under ad from your site?  Does Google rank your site higher?  Google’s answer to this question is relatively simple.  The answer is no!  If you are experiencing differences in terms of usability statistics then it is probably more to do with the user experience than anything else.  Google does not penalise our site one way or another for using pop unders.