Setting up your own push notification service is a daunting task. It usually involves writing software and having a server you can rely on to deliver your messages. Yesterday, App.net brought push notifications to the masses. You no longer need to own or lease any hardware or write any code to, say, send push notifications about breaking news.
There are a ton of obvious uses; some are mundane, and some would be incredibly helpful. I would love to see services like GitHub use this to publish service outage notifications, for example.
I’ve gone the mundane route myself and set up new-post notifications for this blog just to test things out. You can subscribe here (or using the button in the footer).