If you look at the WP7 notifications framework, we have taken the approach of a simple framework that is simple to get started with.
There is no explicit registration to use the service for developers and with a few lines of code, you are up and running.
Our integration with the phones start experience, allows you as a developer, to let your application behave like the rest of the platform. Users of your applications will recognize the behavior which will give them a more "I know what is going to happen when I click here..".
Go and get the latest CTP refresh of the developer tools at http://developer.windowsphone.com, with the refresh you will be able to pin tiles to the start experience and send notifications to it. It is really cool.