In 2008 and 2009 I participated in growing the Drupal France community from a dozen of people at a first meetup to setting up a 900-participants Drupalcon Paris. It took multiple realspace events, including a dedicated experimental new event format for helping NGOs, and many, many online conversations with consensus mode on :-)
Since 2011 I'm the community building specialist and co-founder of Museomix, an international community of museum geeks. We focus on setting up yearly community-driven, hackaton-like 3 days events in museums. The museum stays open to the public during the event! We over-design the event pace and milestones, so that real, working hardware prototypes are actually build in 3 days, and can be experimented by the public as new museum experiences.
In 2013, there will be 6 Museomix events in 6 museums in France, UK and Canada, during the same weekend. http://museomix.com