Usability is not something that can be 'tacked onto' a website. Like sales, usability is not an option - it is something that you can choose to ignore at your own peril or you can address it to unlock hidden potential.

Most website usability is the equivalent of a door-to-door salesman chasing you down the street, getsiculating wildly, insulting you, then leaving without saying what he was trying to sell. Usability professionals are angry people because no one seems to think that this is a problem.