More than 200m computers have at least one P2P application installed

"Globally, estimates from file-sharing research firm Big Champagne place the P2P universe at more than 200 million computers with at least one peer-to-peer application installed, and operators of the popular Pirate Bay torrent tracker have identified more than 25 million "peers" who have used their site alone to exchange files."
Source: Mike Harvey, “ Internet pirates walk the plank over free downloads; Four in court over
filesharing site with 25 million users Sweden,” The Times, February 16, 2009, cited the report The State of Music Online: Ten Years After Napster, Pew Internet & American Life Project, June 2009