Nothing too crazy, looking at the changelog. Which is one of the things that makes Backbone great - the functionality is rock solid at this point.

Adding the Collection "update" event is nice. One less thing I have to use a plugin for. The "_isModel()" function is also useful, as I currently use Ampersand.State in some places where I need more advanced model behavior (nested fields, child collections, etc).

So yeah, some very reasonable improvements in this release.