The simplest way that you can measure &#38; tweak usability to your site is to do some basic field testing.<p>Nielsen has an excellent outline for actually testing and applying basic user interface design here<p><a href="http://www.useit.com/alertbox/anybody-usability.html" rel="nofollow">http://www.useit.com/alertbox/anybody-usability.html</a><p>If you have a budget, do it up right.<p>If you don't, rely on family and friends that fit your demographic.