There are some usability studies from Witchita university, which regularly publishes on their findings. If you try the site search [webmasterworld.com] I am sure you can dig up a few threads where this has been discussed in the past.
What aspects do you feel that are working on your site? Which are not? And how does your usability compare to others in your industry? Are there any clear patterns / and or standards?
And, then measure your site: are you following these 'standards' or are you going 'against the grain' and if so, do you have a clear reason to design your site that way?
:) Bit more info would really help get the ball rolling here...and, Welcome to WebmasterWorld.