There are two roots for this word. The first being of course, transfer of data by sneaker, or by foot. Media encompass, but are not limited to, tape, diskette, floppy, CDRom, and Hard Drive. The pros of this method of transfer are numerous. Practically unbreakable security. Unless the courier is physically waylaid, there is no way to censor the packets sent via sneakernet. Cons, bandwidth. It is slow, packet wise, but, Never underestimate the bandwidth of a station wagon full of quarter-inch tapes, or a 747 filled with CD-ROMs. Another reason, it is next to impossible to detect the existence of a sneakernet from the electronic 'internet', or by normal means. Thirdly, it's a way of avoiding the authorities when moving illicit data.

The second root of this word, and the one most common in my paranoid circles is the fact that these nets are very sneaky. It's hard to get access to any given sneakernet (see above), and by the same caveat, you can have fairly trustworthy transfer of data unto the second generation of unknown persons. Mostly, people do not transfer information, or software, or other copyrighted items to people beyond the second generation (friend of a friend, OR I have a friend that would enjoy that...) due to paranoia. This is perfectly understandable.