A week or so ago Microsoft dug into a customer's Hotmail account in order to track down some information about code that had been stolen from Microsoft. Their terms and conditions specifically allowed them to do this, but despite that they received a fair amount of criticism.
With this announcement they have decided to change their policy. Now they will only access private customer data in response to a law enforcement request -- if a similar situation arises, they will ask law enforcement to investigate (by asking them to provide the data).
This is an excellent decision. Our legal system may not be perfect, but it has all kinds of checks and balances built in to prevent abuses and to balance individual's rights against the public need to perform investigations. Rather than inventing their own "legal system" for adjudicating such things fairly, Microsoft is taking advantage of the existing system our society has built up over centuries. Other "cloud providers" (for that is exactly what web mail is) should adopt the same policy.