Late last night the Google Authenticator received a major update on iTunes to version 2.0 which included a new look, and added retina display support for the iPhone 5, but theres no native support for the iPad yet.
It still works the same way as before, punching out login codes in order to access your Google account(s), but as early adopter and iOS developer Steve Stresa discovered after updating:
Google Authenticator 2.0 apparently deletes your accounts. Yet another reason iTunes Connect needs app update rollbacks like Google Play.— Steve Streza (@SteveStreza) September 4, 2013
The update removes your account information, which isn't actually mentioned anywhere on the iTunes app page or changelog either. So you'll be required to pair your account info again after updating.
So be sure you have your account details safely backed up to a mobile number before you hit the update button.