It has been a long time since a P2P network has reached an identifiable 4 million users. While BitTorrent may come close, its highly distributed nature does not allow for an efficient network crawl. The last network to obtain such heights was FastTrack, when back in 2003 this community reached 4.5 million users. Since that time, the RIAA's lawsuits have devastated FastTrack leaving it with approximately 2.7 million users.
While FastTrack continues its middling existence, eDonkey2000 has grown at a considerable rate. According to Slyck's network statistics, eDonkey2000's population has grown by almost 60% since 2004. Specifically, in May of 2004, eDonkey2000 had 1,989,611 simultaneous users. In May of 2005, this number grew to 3,384,112 simultaneous users.
Today, the eDonkey2000 network bypassed 4 million users at approximately 12:00 PM EST. ocbMaurice's eDonkey2000 network crawler hit 4,018,712 estimated users, before settling back to 3,961,050 an hour later. The network statistics provided by eMule concurred with this estimate.
Of course, network crawlers are far from an exact science; however they do provide an excellent indication of a community’s trend over time. As eDoney2000 continues its climb, perhaps it will be the first network to reach 5 million concurrent users.