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.
I believe that as we evolve social software to better serve our needs and the needs of the groups that we are involved in, we need to figure out how to apply an understanding of how human groups behave and work. One useful concept I use I call "Progressive Trust". The basic idea is to model how trust works in the real world, between real people, rather then solely relying on mathematical or cryptographic trust.