If the FBI comes knocking on Google's door and says they have a terrorist under surveillance, and they need to read his email in order to save a busload of schoolchildren from a bomb, should Google let them do it?From the Policy:
[When] We have a good faith belief that access, use, preservation or disclosure of such information is reasonably necessary to (a) satisfy any applicable law, regulation, legal process or enforceable governmental request
About how and when they access your information:
We restrict access to personal information to Google employees, contractors and agents who need to know that information in order to process it on our behalf. These individuals are bound by confidentiality obligations and may be subject to discipline, including termination and criminal prosecution, if they fail to meet these obligations.
That "need to know that information" seems to restrict casual access, with the threat of termination to back it up. All of these are more specific declarations in line with a general "don't be evil" policy.