For intelligent environments to become broadly adopted, they need to employ advanced user interface technologies. Such user interfaces have to provide support for personalization, accessibility, context-awareness, openness for 3^rd-party contributions, agent-based user interfaces and management of user interfaces. In this paper, we introduce the concept of a user interface resource server, and how it supports each of these requirements. We describe related existing systems and how far they go in meeting these requirements, including the global resource server provided by dot UI. Finally, we identify future work.