Also related, Google's Data Liberation Front: http://www.dataliberation.org/

"The Data Liberation Front is an engineering team at Google whose singular goal is to make it easier for users to move their data in and out of Google products."

They provide information on how to "escape" from a particular service ie. download/migrate data from that service. However, I can't find any indication of whether there is a way to permanently delete all your data from their servers.