I've been a moderator/host/forum leader for various bulletin boards and other online communities since the early 1980s; first on CompuServe, later on GEnie and AOL, and then professionally in the early days of Consensus Development. One of the behaviors that happens in online communities and that I rarely see elsewhere is flaming -- where one member writes an extremely inappropriate, typically passionately worded attack on another. Flaming behavior can hurt an online community.
A blog on social software, collaboration, trust, security, privacy, and internet tools by Christopher Allen.
Shannon Appelcline, my colleague at Skotos (an online game company that I founded in 1999), has been writing for several years a sometimes weekly, sometimes bi-weekly column on the topic of game design called Trials, Triumphs & Trivialities (rss feed for all Skotos Articles including TT&T). His latest column Social Software & Gaming: User Content discusses issues of user content and user facilitation that apply both online game communities and social software: