And for anyone for whom accomodation costs may be an issue, I give you:
Couchsurfing. Completely free, and pretty easy. Just sign up and look for a couch to sleep on near where you are going. They seem to do some sort of background checks on hosts, and the only other catch is that you kind of have to hope that someone near where you want to go is signed up on there and hosting a couch.
Still, worth a look once we determine the bases for each area of the world.
Or we could just use Skype.
Yeah, but 2 things:
1. You can only have so many people on Skype at once (and it's not free in conference mode), and not everyone may have a mic. So, from what I've seen the plan is to set up bases across the world where people will gather (I'm guessing hotel rooms and suchlike) in small groups, so that everyone can get on conference for cheaper.
2. I doubt that the people who will be hosts for the bases will be willing to let large groups of people stay at their houses, so accomodation would be an issue (If the cam/mic sessions I've had with Pterano, Vonboy and TFM are anything to go by, an all-day meetup is probably not a good idea). Enter Couchsurfing. People can get a couch nearby the bases and travel there for the days.
EDIT: Another little point worth mentioning: The little GoF chatroom that's been set up, it allows for cams and mics, as well as conferencing, and is browser based. So this could be a better alternative to skype