Below the standard text I use for these kinds of things. My special interest is in modeling user's value for community based on their contributions and especially the interactions of the community with these contributions.
standard text:
Thieme Hennis (1981) is a PhD researcher in the Systems Engineering Group of the Faculty of Technology, Policy, and Management of Delft University of Technology. Before joining the university, he was involved in the development of social software to support professionals in their day-to-day tasks at Peers Communities and Filtering (http://aboutpeers.com). In his research, he focuses on reputation as a social currency in online professional communities. More specifically, he researches the influence of reputation on interaction and contributions in communities, and focuses on building reputation standards that support the exchange and creation of knowledge in learning communities, improve relevancy of recommendations, and sustain self-organization.