Form interaction plugin inspired by Vidget's 'Single-Use JQuery' Plugins post: http://www.viget.com/extend/single-use-jquery-plugins/

clonableFields.jquery.js

(function($) {
  $.fn.cloneableFields = function() {
    return this.each(function() {
			var container = $(this);
      var fields    = container.find('li:last');
      var label     = 'Add another ' + fields.find('label').text();

      container.count = function() {
        return this.find('li').size();
      };

      // When link is clicked, add a new set of fields and set their keys to
      // the total number of fieldsets, e.g. instruction_attributes[5][name]
      var addLink = $("<a/>").text(label).click(function() {
        html = fields.html().replace(/\[\d+\]/g, "[" + container.count() + "]");
				$(this).before("<li>" + html + "</li>");
        return false;
      });

      container.append(addLink);
    });
  };
})(jQuery);