gistfile1.js

Arrayobservers = SC.Application.create({

  NAMESPACE: 'Arrayobservers',
  VERSION: '0.1.0',

  store: SC.Store.create().from(SC.Record.fixtures)
  
});

Arrayobservers.objects = [SC.Object.create({foo: 1}), SC.Object.create({foo: 2})];

Arrayobservers.objectsController = SC.ArrayController.create();

Arrayobservers.contentNotifyingObjects = SC.Controller.create({
  objectsBinding: SC.Binding.oneWay('Arrayobservers.objectsController.content*[]'),

  // or perhaps this instead of the other one.
  //objectsBinding: SC.Binding.oneWay('Arrayobservers*objectsController.[]'),

  computedProperty: function() {
     if(this.get('objects')){
         return this.get('objects').getEach('foo').get('@sum');
     };
  }.property('objects')  
});

Arrayobservers.valChecker = SC.Controller.create({
  valBinding: 'Arrayobservers.contentNotifyingObjects.computedProperty',

  valObs: function(){
     console.log('val has changed: ' + this.get('val'));
  }.observes('val')
});

console.log('should now see computed property output twice');
SC.RunLoop.begin();
Arrayobservers.objectsController.set('content', Arrayobservers.objects);
SC.RunLoop.end();

SC.RunLoop.begin();
Arrayobservers.objects.firstObject().set('foo', 5); 
SC.RunLoop.end();