I've found that user groups often fall into a pattern of lecture style presentations with slide shows. Since it's usually difficult to find presenters, often it ends up that after a while whoever founded the group speaks repeatedly. This leads to burn-out and isn't sustainable even if you're fortunate enough to have presenters who are skilled public speakers. It's also simply not a very good way to learn; your mind is a lot more involved in a when engaged in active discussion.
This is why at the Seattle Clojure group we follow a different model that focuses on code and participation. A few months ago at the ClojureWest conference I gave a short talk (PDF) explaining the motivation behind this style. I call it "swarm coding".
The Socratic Method is a form of learning that centers around getting people to ask the right questions rather than just telling. It's often used in group settings with classical education methods, and I've found it's a great way to run a user group meeting as well. If you can get everyone hooked in to participate in a shared editor session and come up with an idea for a small project, you can collaborate in a unique, engaging way and learn a lot.
We've found SSH, tmux, and Emacs to be a great combination for this. The host prepares his machine with a new user created just for the purpose of swarming, and everyone is given the username, hostname, and password to log in over SSH.
$ ssh email@example.com
$ tmux attach
Once logged in, running tmux attach allows a user to join an in-process session started by the host, and control can be passed around as discussion progresses. If someone has an idea for how to address a certain problem, they can just try it out straight away. While there are more complicated setups that can allow for each user to edit independently, we've found that is usually not what you want. If you have a discussion going on, you want a single point to focus on. It's really hard to track what's happening if you have multiple independent edits happening simultaneously.
Usually skill levels vary widely in group settings like this, so it's important for the facilitator to be able to gauge them, usually by just getting quick introductions from everyone in the group beforehand. The temptation is often for those that really know their way around to just power through and write some slick code, perhaps pausing to explain a particularly subtle technique. It's more rewarding to let control pass around the group and try to keep everyone involved, but it can be difficult.
It's probably a good idea to dedicate a meeting to a tooling workshop at first to get people started. Especially with Clojure the initial setup can be intimidating, so the newcomers find it valuable to get help just getting the basics working on their laptops. While I don't recommend newcomers try to learn Emacs as their main editor at the same time as picking up a new language, it really makes collaboration over SSH much easier, so basic familiarity is helpful.
I've coded up some scripts to automate setup of swarming sessions. It handles getting basic dotfiles in place and provides instructions for how to join a session when people log in. Right now it only supports Clojure, Leiningen, and Emacs, but there's no reason it couldn't be extended for Vim or other languages.
Update: I have another project called Syme which handles setting up pair/swarm nodes on EC2. In most cases this is a lot simpler than running the tmux session on your own machine, though it may not always be feasible depending on the quality of the network.
There are a few things to watch for here. First of all, we've only tried this with groups of up to 12 participants. Group dynamics break down when things get larger, so you may want to split up into groups. You could try splitting a project into independent parts that could be coded by each group if your project divides naturally this way, or you could try both tackling the same problem and comparing solutions at the end.
Picking a project to try is also tricky. You want it to be somewhat useful and not contrived, but you also need it to match the skill level of the group and still be able to make progress on it in a couple hours. It's a lot of fun if you end up with a project you can publish to Clojars or Heroku at the end.