We're rebuilding some pieces of our editor in Poll Everywhere and to date, its the most sensible approach to JS MVC that we've seen. Frameworks like Cappuccino and SproutCore make it really hard to control the look and feel if your application and take an "all or nothing" approach whereas Backbone.js goes with the "grain" of the web letting you mix-and-match whatever JS libs you want to use for your project.
We're rebuilding some pieces of our editor in Poll Everywhere and to date, its the most sensible approach to JS MVC that we've seen. Frameworks like Cappuccino and SproutCore make it really hard to control the look and feel if your application and take an "all or nothing" approach whereas Backbone.js goes with the "grain" of the web letting you mix-and-match whatever JS libs you want to use for your project.