Backbone surely has good parts we were able to use right away: the event-driven concept in general (the Backbone.Events mixin), the Model with its attributes and change events, the View with its conventions (element reference, the Render pattern, free templating). Even if we couldn’t use all parts of Backbone it was a good idea to built upon the Backbone code and these common practices.

We dropped the Backbone.Router completely, but Backbone.History in turn is quite decent for HTML5 history and hashchange handling, so we’re relying on that.

Of course we could have borrowed only the code from Backbone we might need, but I think in the long run it’s a good idea to build upon an existing library or framework which is actively maintained, even if it doesn’t provide everything you might need at the moment. So writing all code ourselves wasn’t really an option for us.