This is fairly well researched wrt banners. Basically once users associate visual elements with noise, the will start to automatically filter them to the point of not being conscious about their existence.

In a even broader scope, Jakob Nielsen has shared lots of data from his eye tracking usability studies that show just how little attention users pay to online content [1][2].

[1] http://www.nngroup.com/topic/advertising/

[2] http://www.nngroup.com/topic/eyetracking/all/