User data is saved in Google App Engine data store. No identifying data, nor user passwords, are saved at any time. Users are identified by app with unique id generated on registration time and Google account id, which cannot be used to retrieve personal data.
Following user information is saved:
Notification data is saved for later reading from app. Data is saved in same data store as user data. Following message data is saved:
Only app developer has access to App Engine data store, and no information is given to third parties. Initial authentication is provided by Google, but no other data is sent directly to Google.