I haven't seen this code yet, but since you brought it to attention, `listeners[ event.type ]` is an array. So it's safer just to...
```javascript
for(var i = 0, l = listeners[ event.type ].length; i < l; i++)
```

There's a few other optimizations I may do in this file, in another pull request. Backbone.Events is a great model to follow for performance, across most, if not all modern platforms. I recently ported it to a proprietary engine pretty easily.