Ed Felten and Randy Picker [who] point to an interesting ruling from the 6th Circuit Court of Appeals: Because people have a reasonable expectation of privacy when they communicate over e-mail, the court ruled that the government must obtain a search warrant to get your e-mail from your ISP.
The logic of the ruling is the same as the logic behind requiring a warrant for a wiretap or to search a mailed letter or package. Some legal scholars think the ruling is likely to be overturned for technical reasons, but I for one hope the legal reasoning ultimately prevails.
Joshua Rosenau spends his days defending the teaching of evolution at the