Data centres have been the primary focus of energy efficiency researches due to their expanding scales and increasing demands of energy. On the other hand, there are several orders of magnitude more end-users and personal computing devices worldwide. Even the modest energy savings from the users would scale up and yield significant impact. As a result, we take the approach towards energy-saving by working with the end-users. We recognise that users of ICT systems are often unaware of their power usage, and are therefore unable to take effective actions even if they wanted to save energy. Apart from energy awareness, the majority of end-users often lack of sufficient knowledge or skills to reduce their energy consumption while using computing devices. Moreover, there is no incentive for them to save energy, especially in public environments where they do not have financial responsibilities for their energy use. We propose a flexible energy monitor that gathers detailed energy usage across complex ICT systems, and provides end-users with accurate and timely feedback of their individual energy usage per workstation. We tailored our prototype energy monitor for a 2-year empirical study, with 83 student users of a university computer lab, and showed that end-users will change their use of computers to be more energy efficient, when sufficient feedback and incentives (rewards) are provided. In our measurements, weekly mean group power consumption as a whole reduced by up to 16%; and weekly individual user power usage reduced by up to 56% during active use. Based on our observations and collected data, we see possibilities of energy saving from both hardware and software components of personal computers. It requires coordination and collaboration between both system administrators and end-users to maximise energy savings. Institutional ‘green' policies are potentially helpful to enforce and regulate energy efficient use of ICT devices.