[rdl]

It's per-device, not per account (I know the guy who developed it for Google; one of the smarter people in the industry).

It uses protected storage for the credential so it isn't backed up to iCloud, either. Sadly on Android they don't have the same security features available, due to limitations in the OS; it would be fun to talk to Samsung and make a "actually secure Google Authenticator" specific to the S3/S4 since they have a security element.

If you do want it on multiple iDevices, you need to do that at setup time, by copying the secret manually.

[jis]

The Duo-Security people, who have an Android Token claim to use the secure element in NFC enabled phones. It is a TOTP token and can be used just like the Google Authenticator. You don't have to use Duo-Security's system to use it (though there system is worth looking at if you are rolling out your own authentication system).

[rdl]

URL? I don't see anything about their android "duo push" or "duo mobile" client supporting the secure element, but their website is designed around the kind of people who buy $3/mo authentication systems (enterprise, not saas developers).