Urbain Airship: a webhook based service for Iphone 3.0 Push Notification

This morning I discovered a new recipe on Google App Engine Cookbook to send out Iphone 3.0 Push notifications via Google App Engine. In fact, the recipe makes use of a service called Urban Airship. They provide a free service that allows to send upto 5000 Push notifications a month. For larger volumes, the price seems reasonable. Image now that all content producers become pubsubhubbub (the pseudo realtime webhook based enabled publish/subscribe protocol proposed by two Googlers) enabled and maybe we scratch the surface of the future internet architecture that will drive the realtime web. Who knows?