Opened Email, ISPs and Search Warrants: What Does Federal Privacy Law Permit?
According to recent blog post on the Volokh Conspiracy, the federal government is currently involved in a dispute with Yahoo over whether or not they can compel an ISP to hand over opened email without a probable cause warrant.
The author of this particular article seems to think this case could overturn federal statute in such a way that the Supreme Court will, ultimately, become involved.
This should be an interesting case to watch.