In most online communities, 90% of users are lurkers who never contribute, 9% of users contribute a little, and 1% of users account for almost all the action.
So, what can be done about this? How can the site owner increase user participation? The short of it, according to Nielsen, is that you can't.
I have found that posts that have comments get more comments. It seems as people are more tempted to respond to comments than the original post; or posts with comments than posts without any comments.
Sysomos also found that 80.6% of Twitter users have made fewer than 500 tweets, which likely points to the relative newbie status of the average Twitter user. Also noteworthy is that 22.5% of users are responsible for 90% of all tweets.
It will be interesting to see what happens over time - do Twitter stats start converging to the expected 90-9-1 spread?