Thanks for your input. As you probably realized, my post was more about a strategy for apps that feel more like desktop apps, where once you're logged in, you're not really moving around from page to page at all. In my case it was a chat app where the whole app was useless without JS.

It's an interesting thought, though. However, I don't know if I'd see the need for something like backbone on any site where I was trying to support non-js browsers.