Also, I’ve been working with AngularJS recently. I understand the benefits of a front end framework to keep data in sync throughout your client. Angular fans tout the benefits of a SPA (single page application) framework.
As someone who strives to separate the structure (HTML) from the scripting (JS), Angular feels too tightly coupled to me. Angular works by tagging everything with [cci]ng-[/cci] and letting the magic work behind the scenes. The application dependencies are hardcoded everywhere in your HTML, and there is no way to swap your framework without changing your HTML drastically.
I’ve worked with Backbone in the past, and now I’m trying out Angular. At some point, I’ll probably try out Ember. I’d like a front end framework that plays well with Rails, so perhaps Ember will be fun.