I've been using Google App Engine for a while now, and it is hard to go back to traditional java webapp development given how easy it is to deploy a demo version for a customer, and how great some of the tools provided in the App Engine SDK are.
Among those tools is the Channel API. It offers push messaging with only a few lines of code. There are some drawbacks (mainly regarding the reliability of the communications) but it still is a great tool to provide real-time notifications to the user.
Now, I read Angular JS provides some support for Comet notifications, but nothing for the Channel API. On a project I'm developping on my spare time there's this need to send chat messages to various users.