Latest stable docker + Ubuntu Precise (12.04) 64bit

Vagrantfile

#!/usr/bin/env ruby

# -*- mode: ruby -*-
# vi: set ft=ruby :

def machine_exists?
  !Dir.glob("#{File.dirname(__FILE__)}/.vagrant/machines/default/*/id").empty?
end

Vagrant::Config.run do |config|
  config.vm.box = "precise-64-docker"
  config.vm.box_url = "http://bit.ly/dockerprecise64"
  config.ssh.forward_agent = true

  unless machine_exists?
    cmd = "apt-get update -qq;
            service docker stop;
            apt-get install -q -y --force-yes lxc-docker"
    config.vm.provision :shell, :inline => cmd
  end
end