It would probably cause more problems than it would fix but a couple things it would help with: chatterbox and voting. Like on Yahoo and Amazon, you could vote silently. Vote and the radio buttons disappear. The vote is counted on the server side but the page isn't necessarily reloaded. Better user experience. Chatterbox could be remotely refreshed every time there is a new "talk."

Problem is, the site is already sluggish most of the time, so the apparent savings would probably just be shunted off to higher loads from talking back and forth with clients; gains would vanish whenever you actually did request a full new page. Plus, it's just not very "Monk-ish" and there are quite a few JSphobes here.