I'm preparing a presentation of QGIS to release of the brazilian QGIS user guide. Thus, I would like insert some information about QGIS in global scale. Something like Tim's qgis-for-humanity presentation, but with updated information. I'm very pleasure if you have something in this direction to send me.
The latest "official" numbers on downloads and distributions are available through http://spatialgalaxy.net/2011/12/19/qgis-users-around-the-world/
Wikipedia has a list of release dates: http://en.wikipedia.org/wiki/Qgis
The developer community is very international and not centered in any specific country. There are different user communities focusing on different language regions like e.g. the German-speaking users which have been holding annual meetings in different Switzerland.