What is sneakernet?
Old term. Before we had networked PC's people would exchange files by copying them to a diskette and hand-carrying the diskette to another computer. Hence the name sneaker-net.
It is a method of network communications invented by a guy known only as "Trannie" ;)
IMO, the use of key logging is legitimate if authorized by a specific warrant for the interception of a suspect's e-mail communitcations. The fact that the Feds have to install something on the target's machine (which takes manpower, and could get them caught red-handed if they do it illegally) serves as a check against the sort of secret blanket surveillance which is possible with systems of the Carnivore type.