I've long been an admirer of Jeremy Bailenson's research at Stanford University's Virtual Human Interaction Lab. His team are behind many very interesting projects researching the social psychology of digital human representation. Nick Yee especially has produced some excellent research output. Bailenson's theory of Transformed Social Interaction is providing a great framework from which to explain some of the findings coming from virtual worlds social psychology research. Here is his fast-paced talk from Metaverse U conference 2008.