This is a great idea and everyone has awesome ideas, but now it's starting to look a little confusing for me.
Just a suggestion: maybe settle on a date and a name and then let everyone decide what they want to do themselves, in their own way, let everyone be creative with it, then there's no problem of anyone feeling like they're being ordered around, and everyone is happy about being able to do what they want to do?
The basic plan is that there will be a meet-up in most big cities/towns, right? It's fairly easy for everyone to then go and work out who lives in their area and discuss what the plans are amongst yourselves on Facebook or on here or whatever.
I think most people already have a general idea of who lives near them, so talk about it with those people and figure out what you want to do on the day, and then you could start putting the word out to non-GDC members in whatever ways you can come up with?
The separate Facebook groups for each place are neat. Everyone seems to have a Facebook, and everyone's been coming up with great and fun ideas and being really thoughtful.
I don't really think leaders are super necessary, everyone is capable of planning and helping out - some more than others, but that's just my opinion. Team work is awesome fun. Y'know. Just an idea.
I can't see it being a very easy task for just a few people to have to be in charge and plan out something that looks to be such a big event.
I could have taken this all the wrong way, but I just really hope it works out well for everyone because it really is an amazing idea.