This paper studies the feasibility and benefits of greening Web servers by using ultra-low-power micro-computing boards to serve Web content. Our study focuses on the tradeoff between power and performance in such systems. Our premise is that low-power computing platforms can provide adequate performance for low-volume Websites run by small businesses or groups, while delivering a significantly higher request per Watt. We use the popular Raspberry Pi platform as an example low-power computing platform and experimentally evaluate our hypothesis for static and dynamic Web content served using this platform. Our result show that this platform can provide comparable response times to more capable server-class machines for rates up to 200 requests per second (rps); however, the scalability of the system is reduced to 20 rps for serving more compute-intensive dynamic content. Next, we study the feasibility of using clusters of low-power systems to serve requests for larger Websites. We find that, by utilising low-power multi-server clusters, we can achieve 17x to 23x more requests per Watt than typical tower server systems. Using simulations driven by parameters obtained from our real-world experiments, we also study dynamic multi-server policies that consider the tradeoff between power savings and overhead cost of turning servers on and off.