[azrealus]

We've been using backbone for few of our projects. Here is a prototype we are working on right now: http://whiteboard.couchone.com/whiteboard/_design/whiteboard... it sits on top of the couchdb/couchapp. We did spend some time evaluating different options before we started (including SproutCore and JavascriptMVC). The main reason we decided to go with Backbone is that it's so much lighter. You can actually open the source and understand what is going on. You can plug in your own UI and templating engine easily. Backbone basically allows you to glue different elements together via Backbone's model/collection architecture (it's almost like a real backbone connecting different body pieces together :)).