The rapid adoption of mobile phones by society over the last decade and the increasing ability to capture, classifying, and transmit a wide variety of data (image, audio, and location) have enabled a new sensing paradigm - where humans carrying mobile devices can act as sensor systems. Human-in-the-loop sensor systems raise many new challenges in areas of sensor data quality assessment, mobility and sampling coordination, and user interaction procedures. To this end, we outline our initial steps in designing an incentive based reputation system for assessing data quality, provide an overview of techniques to obtain fine grained contextual information in mobile situations, and detail feedback mechanisms to enable more interactive and informative sensor systems.