As computer applications become larger with every new version, there is a growing need to provide some way for users to manage the interface complexity. There are three different potential solutions to this problem: 1) an adaptable interface that allows users to customize the application to suit their needs; 2) an adaptive interface that performs the adaptation for the users; or 3) a combination of the adaptive and adaptable solutions, an approach that would be suitable in situations where users are not customizing effectively on their own. In this paper we examine what it means for users to engage in effective customization of a menu-based graphical user interface. We examine one aspect of effective customization, which is how characteristics of the users’ tasks and customization behaviour affect their performance on those tasks. We do so by using a process model simulation based on cognitive modelling that generates quantitative predictions of user performance. Our results show th...