So I’m going through the Getting Started documentation on AppEngine, Google’s new hosted application platform, and I come across this great bit of information.
Reload the page in your browser. Your application redirects you to the local version of the Google sign-in page suitable for testing your application. You can enter any username you’d like in this screen, and your application will see a fake User object based on that username.
When your application is running on App Engine, users will be directed to the Google Accounts sign-in page, then redirected back to your application after successfully signing in or creating an account.
So if that means, what I think it means, when you use the Google user authentication, they aren’t signing up to be a user of your service only. They are signing up as a Google user. The pieces then fall into place why this service is free. Google is getting developers to create applications that will add additional registered users of Google services.