PubSubHubbub. Say that three times fast. If you're not familiar with PubSubHubbub, it's an extension of the RSS and Atom protocol that allows the feed to push content out when it's updated. That's just the sort of technology we should see from check-in APIs like Foursquare and Gowalla.
Want to track your pizza’s progress in real-time? Now you can with Pusher’s real-time APIs and Google Maps. In this tutorial, the guys over at the Pusher blog show you how to build your own food delivery-tracking web app hosted on Heroku.