A number of recent Smart City testbeds and deployments have focused on the use of the Internet of Things (IoT) paradigm and technologies for improving the efficiency of city infrastructures. Building on this work, we have explored the use of IoT hubs as easy-to-use aggregators and focal points for access to emerging data infrastructures of smart cities. A hub can support not only access to infrastructure data, but also participatory sensing and crowd sourced data where city employees and citizens contribute directly to the data infrastructure of a city. In this way, smart cities can realize a variety of new applications created by local entrepreneurs and community groups without the need for ongoing coordination by governments. In this paper, we outline the growing interest in a hub-centric approach to the IoT and discuss our own experiences in building an IoT hub for two Smart City projects, one in the UK and the other in Canada.