No matter how you slice the performance pie, it is clear that to ensure that you have satisfied, repeat customers online, you have to design for speed, feedback, and flow. Offering a consistently fast-loading web site with unambiguous feedback can contribute to a compelling online experience.
Give your users a sense of perceived control by offering them challenges matched to their skills. Use a simple layout with minimal distractions, offer interesting well- chunked and delineated content, and make navigation and performance transparent. Happy users are loyal users who will keep coming back to purchase your products and use your services.
http://elab.vanderbilt.edu/Vanderbilt's eLab research center is devoted to studying the Internet, including flow.
http://www.hcibib.org/HCI Bibliography features a searchable database of human-computer interaction resources.
http://www.humanfactors.com/Human Factors International has an excellent free monthly newsletter on user interface design issues.