Using flash[:notice] doesn’t work so well with AJAX calls. Adding a “js_notice” key to flash has helped me in several places.

  
    respond_to do |format|
      if @question_monitor.save
        format.js {  
          flash[:js_notice] = "You will now be alerted to any new activity on this question."
        }
      else
        format.js {
          flash[:js_notice] = "There was a problem in trying to monitor this question"
        }
      end
    end