The growing trend of using smartphones and other GPS-enabled devices has provided new opportunities for developing spatial computing applications and technologies in unanticipated and unprecedented ways. Some capabilities of today's smartphones highlight the potential of citizen sensors to enable the next generation of geoinformatics. One promising application area for this is social media and its application to disaster management. Dynamic, real-time incident information collected from onsite human responders about the extent of damage, the evolution of the event, the community's needs, and responders' ability to deal with the situation, combined with information from the larger emergency management community, could lead to more accurate and real-time situational awareness. This would enable informed decisions, better resource allocation and thus a better response and outcome to the total crisis. In this context, the US Department of Homeland Security's Science & Technology Directorate (DHS-S&T) has initiated the Social Media Alert and Response to Threats to Citizens" (SMART-C) program, which aims to develop citizen participatory sensing capabilities for decision support throughout the disaster life cycle via a multitude of devices and modalities. Here, the authors provide an overview of the envisioned SMART-C system's capabilities and discuss some of the interesting and unique challenges that arise due to the combination of spatial computing and social media within the context of disaster management.