While there haven't been a ton of users who have shared their thoughts and ideas in this thread, I believe that after reading the replies here, attending a convention is the safest and easiest way to get an MD meetup off the ground.
The problem is how to figure out where everyone is and then choosing a convention to attend without drowning everyone in polls. If you'll take a look at the map below:
Note that any place you see with a tint of blue means there's readers. In my home city alone, for example, there's at least 200 MD users of some kind. Clearly, our readers are mostly concentrated on the east and west coast, with the eastern half of the US slightly winning out in terms of population of readers.
To be as fair as possible, I'm thinking of creating a poll with several big name cons on the west coast, in mid-west, and on the east coast of the US to see where we'd all be willing to meet. While the con that I or other staff decide to attend will probably be the "official" meet up, there's no reason why others can't organize their own MD meetups if they wish!
Thoughts or general comments?