Interesting idea, attempting to crunch all of the requests for a page snippet into a single request. Why do it in Javascript, though?
It seems like you'd be better off with a pre-processor server-side to inline include CSS, Javascript and images, then send the resulting page back for rendering. Javascript isn't nearly as fast as my C++-based templating engine...
edit to add: Also, don't discount the big savings you can get from "302 Not Modified" return statuses, especially on big chunks of content like images. The DUI.Stream image demo they had would get smoked by the 'dumb' version if they allowed the browser to cache the digg dude.