Anita Hamilton/Time has this: Playing in the Darknet.

But darknets are not just for digital music files. Carving out a bit of privacy online has wide appeal; students, community groups and even political dissidents can use these hidden networks to share projects, papers and information. One part of the allure is anonymity; the other is exclusivity. Since participation is limited, file searches don't turn up a lot of junk or pornography. Darknets offer the convenience of the Web without a lot of the bad stuff.

The Darknet as she refers to it here is about private file sharing networks, although some researchers wrote about it last year and included any kind of file sharing as part of their definition. However, I first heard about the Darknet in a lecture at SIMS about two years ago, where it was used to refer to anything that was not listed with search engines like Google, because it was somewhat hidden. But my sense is in recent discussions and in media reports, the Darknet now means private file sharing networks.