I used it a month or two ago and found it unusably slow but recently gave it another shot after they released an update and now it's pretty much on par with Sublime on my system. It might be worth you giving it another go.
Javascript seems to go the opposite way of python: instead of ironing the warts out, it adds them. The DOM-API is nonsensical and ugly? Why not add language features so we can implement it in pure JS? Sounds like a great idea.
While I agree mostly with your point, I think the DOM example isn't going to work. The DOM is a spec and doesn't really have anything to do with JavaScript.
Cool! Though, I think it would work better if items were placed on mouse up, that way you could tell if the user was just trying to rotate the display not and place something.
The problem Backbone.js solves is primarily that of structure and organization. It's not about replacing jQuery, its about how you organize that code and have a clearer separation of interface, data, and logic.
