I believe there are some parallels between Net Nastiness and Road Rage.
1. Both happen when the offender feels physically secure from retaliation (the security of a vehicle, the security of anonymity on the Internet)
2. In both forms, the offender is unaware of the personhood of those he is offending. Often, their personhood is erased by using an impersonal epithet to refer to them ("the beige jalopy", "the @JavaNewbie")
3. In both forms, the interaction between the offender and those offended is fleeting, with a very low probability of any further interaction in life
After recently becoming the unwitting subject of a bout of NetNastiness on Twitter, I realized that for micro-blogging sites, these parallels hold even more strongly than for the more traditional blogs and wikis. In the noisy world of Twitter, spewing a short insult like "@ThatUser is a bumbling idiot!" is the online equivalent of cutting in front of someone, flipping them the bird and then taking the next exit on the highway.
While I'm not sure what's the right way to reduce Road Rage, as far as reducing Net Nastiness is concerned I believe following Martin's suggestions is valuable, nay, necessary. By speaking up, contacting administrators, flagging inappropriate posts (where the technology allows it) and switching away from chronically nasty communities; we can make the Internet a more enjoyable, informative and habitable place for the vast majority of us.