the pool of highly active editors is making one-third fewer edits now than in 2007
Wikipedians who contributed 100 times or more in this month Mar 2012 3429 down 34% from Mar 2007 = 5190
Wikipedians who contributed 5 times or more in this month Mar 2012 34,372 down 36% from Mar 2007 = 54,074
I think the once-active editors are running out of new things to write about. That is a sign of maturity, I suggest. Wikipedia is not a fast-growing teenager any more. ~~~~