This time it was Postini:

March 25, 2013 1:38:00 PM PDT

We’re investigating reports of an issue with Postini Services.

March 25, 2013 2:38:00 PM PDT

Postini Services service has already been restored for some users, and we expect a resolution for all users within the next 1 hours. Please note this time frame is an estimate and may change. (editor’s note: resolution took over six more hours).

March 25, 2013 9:05:00 PM PDT

The problem with Postini Services should be resolved. We apologize for the inconvenience and thank you for your patience and continued support. Please rest assured that system reliability is a top priority at Google, and we are making continuous improvements to make our systems better.