Turn off your PC and BitTorrent from a Linux console with rTorrent
Only noobs BitTorrent from their main Windows or Mac computer! Torrenting uses a lot of system resources and can significantly slow down your computer if you have a few torrents open. Additionally, you don't want to upload lots of data while you play games, or while other people in the house are using the Internet -- and really, leaving your computer on over night to download torrents is rather uneconomical.
The best solution, short of getting a VPS and doing your torrenting remotely, is to install a headless Linux or BSD box and control all of your torrents via the text-only console. Now, this isn't a guide on how to set up your own Linux box (there are hundreds of them online, just search) -- but basically any old, unused computer will do. Ideally you want it to be headless (i.e. without a monitor), so that you can put it under the stairs and so that it draws as little power as possible. If you can't choose a distro, Ubuntu Desktop is just fine.
Once you have a Linux box, log in via SSH and install rTorrent, which is by far the best console-based BitTorrent client -- and there are packages for every popular distro. Next, transfer some torrent files onto the Linux box: you can transfer them from your PC using FTP or SFTP (with Filezilla), or download them directly, via the console, with wget.
From the console, type "rtorrent" and press Enter. Hit Enter again and type in the location of your first torrent file. Press Down to select the new torrent, and Ctrl+S to start it. Ctrl+D stops a torrent, and if you do it again it removes the torrent. For advanced functionality, like setting upload and download throttles, check the rTorrent User Guide (and note that ^ refers to Ctrl).
Once you're comfortable with torrenting via your Linux console, you can turn your PC off at night and let the headless box do all of the work. With a little hacking, you can make rTorrent watch a directory, and automatically begin downloading when new torrent files appear.
Finally, it's worth noting that a Network Attached Storage (NAS) box can also double up as your headless torrent box. Check our guide on how to revitalize your old computers for more info.