Getting any reliable estimates on our community has always been difficult. However, recently, in official Wikimedia Foundation announcements and such (ex. http://wikimediafoundation.org/wiki/Donate/Letter/en?utm_source=2008_jimmy_l...) the number "a global community of more than 150,000 volunteers" appeared. I would very much like to now - what date is it based on?
http://en.wikipedia.org/wiki/Wikipedia:Wikipedians gives 8.5 million registered accounts. Of course many of those are duplicates, but then there are many unregistered contributors... still, my own guesstimate would be at at least half a million - if not several millions - of people who had edited Wikipedia (in any language, ove the past ~8 years). This guesstimate is based on analysis of a small sample of editors I know and how many accounts they've created (which for a vast majority is ONE). Sure, there are sockpuppet vandals, but... do we really have 150,000 volunteers, maybe as much legitimate socks/bots, and over 8 millions vandal sockpuppet accounts???
-- Piotr Konieczny