I've been working on visualizing editor behaviour on wikipedia for the past few months. The presentation below is a sneak peak on some of the graphs alongwith the explanation on reading them. They have some interesting findings.
The monthly decline in active editors in the english wikipedia may be attributed to the old timers becoming less active. We see this across other languages too.
Only the articles in the (beginning - 2007) cohorts continue to see active edit activity.
Editor retention rates are much higher in languages like de(german), zh(chinese), ru(russian) etc.
zh(Chinese) shows an uptrend on many fronts. Active Editors, retention etc).
The presentation - http://slides.com/cosmiclattes/edit-activity-graphs-analysis... The project page - https://meta.wikimedia.org/wiki/Research:Editor_Behaviour_An... The Source Code - https://github.com/cosmiclattes/wikigraphs