Torrent is definitely the most popular P2P networks nowadays. Lots of files can be found on torrent while it's not available for direct download. The nature of P2P which involves file sharing is the main reason why this type of networks grew so fast. One of the biggest Torrent tracker site, TPB has celebrate a milestone by tracking over 1 million torrents. They also had over 10 million simultaneous peers on the trackers, 2.5 million registered users, and also 100 blog post.
They add a nice picture on their home page: