I am not a statistician, but I did throw some numbers together to create an overall metric for the editing growth of en:Wikipedia. The idea is thus: How many "active editors" do we have at any given time, and how much are they actually editing at any given time? Find a way to put both on the same graph and you have a slick graph without getting buried in detail.
http://commons.wikimedia.org/wiki/Image:Wiki_editing_growth_guide.png http://commons.wikimedia.org/wiki/Image:En_wikipedia_overall_editing_growth....
Start at (0,0) and follow the arrowheads that indicate time progression. (Loop-d-loops are possible, but didn't show up.) I used numbers from a toolserver page and did some simple manipulation and plotting.
In short: Wikipedia, as of a year ago, was attracting more editors each month while keeping up an average of 115 edits/month/Wikipedian.
Hope this helps, George meta|en|irc:[[User:GChriss]]