I interviewed with Asana back in October and I got to see an in-person demo of the app Justin shows at the 1:45 mark, a "structured list editor" that he says they use internally to track bugs and projects. It's not just a hello world app they built to test the language, it's a real app they use daily and fast fast fast. After poking around on it with only keyboard shortcuts while discussing UI ideas for a few minutes, I completely forget that it was a web app. It didn't have any of gmail's or google reader's lag, for example, which are the only apps with keyboard shortcuts I use regularly.
They promote offline caching, so I'm betting speediness was because his edits were modifying a local db then going through diff resolution after they displayed.
