This is a small gist for autostarting applications with Awesome Window Manager (http://awesome.naquadah.org/) without the need to use a third party plugin like shifty. It's maybe not nice but works!

spawn_once.lua

-- {{{
--
-- Autostarting for Awesome <3.4!
-- Add this section to the end of your rc.lua
-- configuration file within ~/.config/awesome/rc.lua
--
-- If you're using Awesome 3.5 change: 
--    add_signal -> connect_signal 
--    remove_signal --> disconnect_signal
--
-- Thanks to eri_trabiccolo as well as  psychon
--
function spawn_once(command, class, tag) 
  -- create move callback
  local callback 
  callback = function(c) 
    if c.class == class then 
      awful.client.movetotag(tag, c) 
      client.remove_signal("manage", callback) 
    end 
  end 
  client.add_signal("manage", callback) 
  -- now check if not already running!     
  local findme = command
  local firstspace = findme:find(" ")
  if firstspace then
    findme = findme:sub(0, firstspace-1)
  end
  -- finally run it
  awful.util.spawn_with_shell("pgrep -u $USER -x " .. findme .. " > /dev/null || (" .. command .. ")")
end

-- use the spawn_once
spawn_once("subl", "Sublime_text", tags[1][2])
spawn_once("chromium", "Chromium", tags[1][3])
spawn_once("thunar", "Thunar", tags[1][4])
spawn_once("xchat", "Xchat", tags[1][5])
-- }}}

By the way, in recent versions of awesome you can pass rules directly to the spawn function, like so:

awful.spawn(cmd, {
    tag = mouse.screen.selected_tag,
})

If you want to emulate with_shell just pass cmd = { awful.util.shell, '-c', cmd }.

This will provide more correct behaviour, i.e. set the tag for the correct process if several are spawned simultaneously) and maybe also set the tag for all windows if the process creates more than one (I didn't test).

Also, it simplifies the code by a good deal since you don't have to manage signal handlers manually and you don't need to know the window class name in advance.