This article by Henrik Olsen suggests to design navigation systems in webistes to be much more prominent:
Most web development projects put a lot of effort into the design of navigation tools. But fact is that people tend to ignore these tools. They are fixated on getting what they came for and simply click on links or hit the back button to get there.
Olsen quotes the studies of the Visual Cognition Lab of the University of Illinois where people attending certain features where unable to recognize unusual things properly (inattentional blindness). There is a follow-up to these experiments by Ronald A. Rensink.