using_xml_builder_to_gen_json_and_yaml.rb

  def render(opts = {}, extra_options = {}, &block)
    if opts[:to_yaml] then
      headers["Content-Type"] = "text/plain;"
      render :text => Hash.from_xml(render_to_string(:template => opts[:to_yaml], :layout => false)).to_yaml, :layout => false
    elsif opts[:to_json] then
      # headers["Content-Type"] = "text/javascript;"
      render :json => Hash.from_xml(render_to_string(:template => opts[:to_json], :layout => false)).to_json, :layout => false
    else
      super opts, extra_options, &block
    end
  end

# Now, you can call something like:

respond_to do |wants|
	wants.html
	wants.xml { render :layout => false }
	wants.yaml { render :to_yaml => "nodes/show.xml.builder" }
	wants.json { render :to_json => "nodes/show.xml.builder" }
end