This special issue of The Electronic Journal of Communication is guest edited by Barbara Warnick and Laura Gurak. About the issue:

Abstract. Essays included in this issue are case studies of rhetorical expression as it occurs online. We take rhetoric broadly to mean expression for an audience in a particular context designed to motivate audience members to see or experience things in certain ways. Some of these case studies are ethnographic explorations, while others raise questions about the uniqueness of online expression. All of them use the case study or specific experience as a starting point to discover more about how online expression takes place. As such, they are, and are intended to be, suggestive and heuristic.

I'd like to check out some of the essays, but it's not open access. :(