Google recently released a version 2.0.0 update to its Google Authenticator iOS app, which allows customers to use 2-step verification on Google accounts and on accounts with compatible 2-step verification systems.
There are numerous reports of this update deleting account entries in its app store reviews, on Hacker News, and on Google's bug reporting system.
Until more information is available, I strongly recommend avoiding this update. I would guess that Google will remove the update from the app store as soon as possible, and address the data loss issue in an update.
Update: Google since removed this version of the Google Authenticator from the App Store, and later released an update that addresses this problem.