It is possible to take advantage of the idiosyncrasies of the "average user" in the design and planning of your web site. Doing so not only produces a user friendly site, but also helps you accomplish the goals for your site. A survey of the things you can do on your site and the things you might want to avoid is available from Christopher Heng's article:
Is Your Site Ready for the Average User? (thesitewizard.com)