You may have heard it referred to as 80:20:10, the Pareto effect or something similar. I'm talking about the phenomenon that only a small proportion of your community or network are active contributors, the remainder being 'lurkers' or 'freeloaders'. An obvious example is the ratio of Wikipedia contributors to readers. 
One would think that getting the majority or all your community members to be active would be a good thing. However, crowdsourcing research by Zoran Levnajic at the University of Lubljana has shown that there is an optimum level of participatory effectiveness. Counterintuitively, it's not to get everyone to participate.
"Modern information technologies allow for massive number of subjects to be involved in a more or less spontaneous way. We introduce a modeling framework through which we study the effectiveness of crowdsourcing in relation to the level of collectivism in facing the problem. Our findings reveal an intricate relationship between the number of participants and the difficulty of the problem, indicating the the optimal size of the group"
With typical active-contribution rates for networks at around 10%, clearly efforts to increase participation are necessary and worthwhile. We can however take some comfort from this study showing that having a large proportion of potential contributors or consumers (I prefer these terms to the pejorative 'freeloaders') is actually a good thing. 
Which of your networks get close to Levnajic's magic 50% active participation rate?