app.js

$(document).ready(function() {
  $('.model-listing form.edit-comments').attach(Remote.Form, {
    dataType: 'json',
    success: function(json, status){
      if (json.comment){
        var parent_model = $(this.element[0]).parents('.model-listing');
        parent_model.find('.model-comment').text(json.comment);
        parent_model.find('.model-comment').show();
        parent_model.find('form.edit-comments').hide();
        parent_model.find('a.edit-comments').show();
      } else {
        alert('Your comment could not be saved.');
      }
    }
  });
});

some_controller.rb

class SomeController < ApplicationController
  def update
    if @model.update_attributes(params[:comment])
      render :json => {:comment => @job_sheet_listing.comment}
    else
      render :json => {:comment => false}
    end
  end
end