I'd love to know what people think the current "state of the art" stack is for rich and highly scalable web applications, something that has been proven to work great in production by big projects. Is it nginx + Rails + Backbone? When I think of fast rich web apps, Facebook and StackOverflow come to mind, and as far as I remember, neither use the above-mentioned tools (not that it means they're bad in any way).

Just a couple of years ago Rails-generated HTML pages were super hot, and now people are almost insulted if you don't have a fairly complex Javascript framework running the show.