There's a really interesting video with @dhh talking about his thoughts on client-side MVC frameworks with Rails.

He goes into some detail about Pjax and 37signals caching strategy so that partial page updates are snappy and that gives you an experience much like the client-side frameworks without the added complexity.

After working with Backbone.js for a while now I agree with him that development experience of client-side views isn't nearly as nice as generating the views from rails.