Actually, Carnivore has been used approximately 25 times (the FBI says) before August 2000. All the FBI needs is a warrant to use Carnivore against somebody. A warrant for the wiretaps on your email can only be given by a Federal District Judge or higher (normal warrants can be issued by regular judges). In Britain, the Regulatory Investigative Powers bill mandates the use of "carnivore-like" boxes at all ISPs. IN Russia, SORM requires all ISPs to forward all traffic to the FSB (aka KGB).

FBI's Carnivore Info