Things Not To Do
Be narcissistic. Don't talk about what you had for lunch or how you're peeved that one more of your flights got delayed. It's selfish clutter, and serves no larger purpose. We all have lunches and delayed flights.
Gossip. Why on Earth would you want to be publicly identified as a rumormonger?
Be unsubstantiated. Your unsupported, shoot-from-the-hip, fact-and-logic free arguments and opinions are really uninteresting and unhelpful. If you're not willing to do the homework necessary to back up your points, don't bother making them.
Mock others or launch personal attacks. I had a friend who walked out of his performance review and tweeted about his boss's bad cufflinks. I thought this was a deeply bad idea. So are flame wars and trolling. Debates and disagreements are vital components of E2.0 communities, but like Samuel Johnson said, "honesty is not greater where elegance is less."
Discuss sex, politics, or religion. My dad tells me that these were the three taboo topics in the officer's mess when he was in the Navy. They seem like good taboos to keep in place with E2.0; it's just too easy to upset people and start nasty, pointless fights on these subjects. Of course, this these taboos don't really apply if you work at Playboy Enterprises or Focus on the Family.