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.
Some developers don't just love code that runs--they also like to get out and run, themselves. And, because they're developers, they love to collect statistics and track their progress over time. If you're one of those people, good news: online service MyFitnessPal has provided the MyFitnessPal API to help its users bring together all their data from various devices and apps in a single place.