MediaPost Publications 8% of Internet Users Account for 85% of all Clicks 10/13/2009
The results of an update to the comScore highly publicized "Natural Born Clickers" research, conducted two years ago with Starcom USA and Tacoda, indicate that the number of people who click on display ads in a month has fallen from 32% of Internet users in July 2007 to only 16% in March 2009, with an even smaller core of people (representing 8% of the Internet user base) accounting for 85% of all clicks.
via mediapost.com
Seth has a good comment on this. It's just not worth optimising your website for ad clicks - there has to be something else.
http://sethgodin.typepad.com/seths_blog/2009/11/the-unclicking-84.html
