Ninety Percent of All Usability Testing is Useless
http://www.adaptivepath.com/publications/essays/archives/000328.php

Becker, Lane
Adaptive Path
2004

Abstract:

Ninety percent of all usability testing performed on Web sites is useless. This is not to say that it doesn’t have a significant role to play in user experience design. When done right, usability testing will improve your Web site and your development process, but the current culture surrounding Web site usability testing is such that it rarely benefits the design. Worse, this misapplication can undermine the acceptance of this important technique throughout an organization.