I have a constantly running server that would be a perfect on which to run torrent downloads. The only catch is that the server is headless -- it has no monitor or keyboard. To overcome this obstacle, I use rTorrent as my torrent client, and GNU Screen so that I can disconnect my terminal session and leave rTorrent running.
Torrent is a great way to transfer large files very quickly. However most torrent clients are gui based and have quite some impact on system resources (e.g. Azureus). rTorrent is a lightweight client running from the terminal. Being able to run it in a screen session (also upon boot) makes it ideal to also control it from a remote location.