Beginning on June 26, our Appirio Search for Google Docs product displayed an error to all customers when attempting to sign into Google.
We determined this was caused by a bug in the Salesforce Proxy and filed a case with Salesforce. The Proxy enables Javascript hosted by Salesforce (S-Controls) to call out to remote services hosted on non-Salesforce servers. In this case, the Proxy was failing to pass requests from the browser to our servers, which enable the integration between Salesforce and Google.
As of July 21 at 9 am this problem has been resolved by Salesforce support.