Customization happens when the user tells the computer what he or she prefers to see. Examples include: * Changing a news site to display the user's hometown weather forecast upon future visits to the homepage. * Changing an automobile vendor's site to display a particular car model with specific color and feature options, along with the customized car's list price. Most auto sites now feature such configurators. Our study looked at sites with and without customization to see whether there are any marked usability differences. We also separated interface customization sites from those with product customization. Interface customization task success matched that on non-customization websites, with an average completion rate of 83%. However, product customization sites averaged only 66% task completion a significant gap.