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.
As someone who now has over 171 professional "connections" in my LinkedIn Profile, 198 "friends" on Orkut, many more non-intersecting friends and acquaintances on Tribe.Net, LiveJournal, and other social networking services, as well as a plethora of correspondents that I only interact with via email, I am trying reconcile a mismatch between my connections and my own Dunbar Number. How do I maintain meaningful relationships with over 300 people?