Does this shot from the Apple keynote today look familiar?
If you are familiar with Twitter or XMPP it should. Out of all the things they talked about I think this might be my favorite. It looks to me like it’s a diagram of a publisher/subscriber relationship, where the iPhone is the subscriber and the 3rd party service is the publisher. An umbilical cord to the mothership that enables it to receive data from publishers at any time.
Apple introduced this to solve the IM problem–how do you notify somebody of something if they’re not looking at your application, without having the application running? It’ll be interesting to see where they take this. Having a publish/subscribe service built into the operating system could potentially be extremely powerful and enable all kinds of new applications based on it.
This plus the momentum behind a Twitter-like conversation cloud, which is based on the same pubsub model, gives me the sense that the time is right for event-based applications. I would be shocked if Apple doesn’t in fact build a Twitter clone on its MobileMe service.
I posted on the topic of personal pubsub a lot over a year ago, but it hasn’t gotten much buzz lately and really deserves some re-hashing. XMPP pubsub is one of the areas of emerging technology that really excites me, because it solves the realtime aspect of distributed applications very well.
It’ll be interesting to get my hands on the SDK and find out what kind of messages you can send to user’s iPhones. Hopefully they’ve made it extensible enough so that you can send a custom payload that your application can consume and use to add additional value. If so, this could be the beginnings of a pubsub model that touches the consumer, or what I like to call a message bus for the rest of us 
(If you haven’t seen the keynote, they’re billing their MobileMe service as "Exchange for the rest of us", so I’m not just being corny
Yet one more reason why I must have this phone!
Update: WebWare has a somewhat interesting analysis of other potential uses of this feature such as tracking application popularity, I’m a little bit confused as to how this works beyond tracking downloads, however.
