A reminder that Google will enable IPv6 permanently on June 6th, 2012 at 12am UTC.
The countdown to IPv6 was announced back on January 17th, 2012 here. This was done for 24 hours a year ago and we did not notice any major disruptions for Apps customers.
Customers with SSO IP Whitelists and IPv6 capable equipment need to ensure that their SSO whitelist configuration contains their IPv6 network segments (if applicable). The SSO Help Center article is linked here.