I just finished adding PubSubHubbub support to the web app. It's pretty cool. It allows feeds to designate a "hub" that interested parties (subscribers) can contact to request notifcation of feed updates. When a publisher puts new content in a feed they notifiy the hub (ping it via HTTP post) and the hub fetches the feed and will send the new content to the subscribers. This all happens very quickly. I did a PubSubHubbbub demo video to demonstrate how quickly transaction takes place.