I use utorrent on PC, ctorrent on Linux (seedbox), and transmission on Mac. I usually seed to a ratio of 1-2, unless i see that the number of seeds is greater than the number of peers, in which case I might stop before the ratio gets to 1. Typically, the more I like the torrent, the more I'll seed. If it's a torrent that I *really* like, then I might seed to a ratio of 10 or more. If it's a torrent that I created, then I seed ad infinitum, or at least until there are no more peers or I delete the file.