Are there any problems with security or compliance with the rules for storing user data (name, email address, address, phone) in the Google App data store?
In its privacy policy, Google declares that it adheres to the US Safe Harbor privacy principles , which states:
Organizations should take reasonable precautions to protect personal information about loss, misuse and unauthorized access, disclosure, alteration and destruction.
If your application has to comply with certain compliance rules that deal with data storage, you probably cannot use the Google engine because you do not have control over what Google does inside.
This is probably the same thing for other hosting providers.