Hi all,
this new blog post might be of interest to this list: https://blog.wikimedia.org/2015/04/30/how-many-women-edit-wikipedia/ On the occasion of the recently concluded Inspire campaign, it gives an overview over existing data that informs what we know about the size of the gender gap, including gender-related results from the 2012 WMF editor survey that some people on this list have been asking about. Most is about Wikipedia editors, but there is also a bit about Commons and Wikibooks. The post also lists some important caveats that should be kept in mind when discussing these percentages.
(Many thanks to Aaron Shaw, Skud, and Siko Bouterse for their help with this post.)
While I was at it, I also created a new documentation page for the 2008 UNU-MERIT survey which put the gender gap on the map, and still received quite a bit of attention recently: https://meta.wikimedia.org/wiki/Research:UNU-MERIT_Wikipedia_survey