How can no human see the data that Google has? Google is not a magical place where machines cannot be compromised.
>To my knowledge there has never been a hack of Google's data or any leak connecting any user's identity to PII.
The Snowden leaks say otherwise. http://www.slate.com/blogs/future_tense/2013/10/30/nsa_smile...
>This is ridiculous FUD, you're not compromising anybody's privacy by letting google drive do an OCR for you.
So it depends on your threat model. If you care about rogue Google employees or other actors with 0-day exploits, then putting information into the hands of Google is a risk.