Many cities in the US have had occasional meetups, but these are often held erratically, and usually without agenda. We've had some notable successes with organizing in New York City recently, and our group even seems set on becoming the first Wikimedia "affiliate chapter" in the United States.
How did we do it? A big table. With: people sitting around it, engaged in discussion. Without: A banquet and drinks setting (unfortunately).
The important thing is to have a clear space where you can hold real group discussion, pursue content projects and educational outreach with other local groups, and open a mini-conference where members can make presentations on their Wikimedia areas of expertise (more on this in later posts).
All you need is someone WP:BOLD enough to organize. You just need to set a date (and stick to it), advertise like hell, write a preliminary agenda, and find the right space. It's not very hard to get ahold of a space with a big table, and it shouldn't have to cost anything to reserve a room. Our first big table meeting was in November at a public library. Our meetings in January and March were in a room at Columbia University, arranged by one of our members who is affiliated there. We've been holding a meeting once every two months, and I would recommend that for other groups as well.
While Wikimedia has been incredibly open to the contributions of volunteers online, there has been relatively little scope for real-life volunteer activities, because of the small footprint of the Foundation on-the-ground. There has been constant talk of a nationwide "US chapter" online for years, but very little progress.
I believe that the solution is not a theoretical bureaucracy of American Wikimedians on Meta or IRC, but rather a diversity of local chapters capable of engaging in real-life meetings and activities on a regular basis. And that extends not just to New Yorkers, but to Wikimedians in all major metropolitan areas, who can all have something to contribute through on-the-ground activities. Indeed, the whole point of this blog is to show that it can be done in other cities too.
And the good news is: You can still have that banquet and drinks setting. We still do, every time, because social settings are a large part of what people come to meetups for. But we do it after the afternoon meeting, when we can take our evening stroll together, and set out for a neighborhood restaurant and some well-deserved laid back wiki-chat.