app.handlebars

{{#view id="messages" isVisibleBinding="App.noticesListController.isEmpty"}}
  {{#collection App.NoticeCollectionView }}
    {{content.body}}
    <a class="hide">Dismiss</a>
  {{/collection}}
{{/view}}

app.js

App.noticesListController = SC.ArrayController.create({
  // Initialize the array controller with an empty array.
  content: [],
  isEmpty: function() {
    return this.getPath('content.length') == 0;
  }.property('content.length').cacheable()
});

App.NoticeCollectionView = SC.TemplateCollectionView.extend({
  contentBinding: 'App.noticesListController',
  tagName: 'div',
  classNames: ['message', 'notices'],
  itemView: SC.TemplateView.extend({
    tagName: 'p',
    classNames: ['notice'],
    mouseDown: function(evt) {
      var notice = this.get('content');
      notice.destroy();
    }
  })
});