I've often spoken to clients, colleagues and conferences about the "rule of thumb" in terms of community or network engagement. This could be engagement in a social network, a community content portal or an enterprise venture. It's a little Jack Walshian in it's approach, but serves to illustrate the point.
* 70% just watch
* 20% actually participate / create content
* 10% shouldn't be there in the first place.
(UPDATE: 1% hide somewhere in there. The troll race! Destructive personalities who leap on hapless participants, causing literary carnage...)
While it isn't backed up with any research or scientific method, it does guide expectations in terms of participation, how to engage, who to engage, how to segment and most importantly, how important your "social kingpins" (the 20%) are for longevity.
The article sites Forrester Research and splits participation as such:
To help companies target their Internet strategies, Li and Bernoff have organized Forrester research into a "social technology ladder," which classifies consumers based on their participation in various types of social networking. At the lowest rung of the ladder are the "inactives," some 44% of all U.S. American adults who were online in 2007. Higher up are the "joiners," the 25% who visit social networking sites like MySpace; collectors, an elite 15% who collect and aggregate information; and critics, those who post ratings and reviews as well as contribute to blogs and forums. Only 18% of all online Americans actually create content, publishing an article or a blog at least once a month, maintaining a web page or uploading content to sites like YouTube.
Food for thought...