Nielsen is well known for his Jakob's Law of the Web User Experience, which states that "users spend most of their time on other websites."

http://www.useit.com/alertbox/9605.html

Yes, any designer of any one website has to plan for an audience that has already developed habits of viewing on other websites. That's why banner blindness

http://www.useit.com/alertbox/banner-blindness.html

is such an important issue in website design. Don't put ANYTHING on your site that looks like a banner advertisement if you want site viewers actually to see it.