Customization - an attribute that lets users take control and make changes to the presentation and functionality of the interface - is becoming a hallmark of today's interactive media devices. What do users experience when they change interface aspects like fonts and colors, skins on mobile phones, speed dial numbers, privacy settings on social networks and different command menus in software? Do they feel in control? Do they see the customized interface as a reflection of who they are? More importantly, is the feeling of being in control a major driver of usage, or does sense of identity - a personal connection with the interface - prove more vital? This paper discusses the psychology of customization, reports an empirical user study designed to explore the relationship between customization, sense of control, and sense of identity, and outlines implications for design of customizable interfaces based on the findings.