I noticed this cool new method added to the _Widget class... (the internal doc is very helpful BTW)

I have a small suggestion. The code could be simplified, see below:

placeAt: function(/* String|DomNode|_Widget */reference, /* String?|Int? */position){
   if(reference["declaredClass"] && reference["addChild"]){ 
      reference.addChild(this, position); 
   }else{ 
      dojo.place(this.domNode, reference, position); 
   } 
   return this;
}