Crowd Psychology – This is what happens when individuals find that they have more power as a group than when they act alone. If you’ve done something that has a bunch of people upset, expect one to post your link, two more to demand to know your name, five more to dig up the information and post it, and a mob to form in front of your door by sundown. Watch this very carefully!

Opinion Leadership – The strongest voice and the clearest communicator comes out at the top of the thread. Others start looking up to that person – sometimes to the point of holding their own opinion until they’ve read the thoughts of the “opinion leader”! This is often the “top submitter” on a social news site.

The Bandwagon Effect – When a large crowd rallies around a certain idea, the idea becomes more popular and attracts more supporters. It’s a snowball!

The Idea Economy – You’ve heard this term bandied around on web marketing blogs. It is, quite literally, an economy. You take out what you pay in. people with nothing to contribute, such as jokers or trolls, find themselves voted to the bottom of the thread while the people with the ideas that speak to people get voted to the top.

Turf Wars – Don’t let the people on Digg know you go to Facebook. Don’t go on Facebook asking about 4chan. Don’t go in 4chan bragging about your MySpace page. And so on. Social web members are starting to get a little territorial, seeing the differences between the various sites as a wedge of “us vs. them”. This can be tricky.

The Herd Mentality – Often decried on the site itself, even by its guiltiest practitioners! Face it – people like to hang out with other people who agree with them. Yes, it makes us all sometimes petty, irrational, and argumentative. But it’s still human nature – ignore it and you go broke!