What a nice combination of tools! I just installed Capistrano and created a capfile. From then on, I could run commands across all my virtual istances in one shot. This setup took just minutes. The only change that I made to my existing instances was to add a capistrano userid. My capfile looks like this:

role :files,

namespace :files do
  desc "Show free disk space"
  task :show_free_space, :roles => :files do
    run "df -h /"

The best thing of all? No XML configuration!