Google continues to push away at improving its Platform-as-a-service offering, the Google App Engine API. It has already seen two minor releases this year with the latest release bringing in much needed updates to the XMPP and Task Queue APIs. An earlier release in the year focused on the High Replication Datastore, that was clearly targeted to mission critical applications.
The XMPP API is a key service available in the Google App Engine infrastructure to allow your application to send and receive messages from any XMPP-compliant messaging service, such as Google Talk. The key features added in 1.4.2 release are to do with Subscription and Presence notifications. Your Application can now get notified if a user signs in and out and when their status changes. Your application can also announce its presence details to the users by sending the application's presence via the sendPresence() call. Optionally, this can include a status message.
The Task Queue API service allows for background processing by inserting tasks (web hooks) into a queue. App Engine will then execute them subject to some criteria. The Task Queue API enhancements include a programmatic way to delete your tasks. Additionally, the API now has a maximum execution rate of 100 tasks per minute and allowing an application to specify the maximum number of concurrent requests per queue.