Deluge
Here is a change that I think would be fairly simple to implement and would make it much easier for some people to manage the seeding of their torrents: an optional column in the UI to track when a torrent last sent out a piece to another peer.
I like to seed things a long time. I have some torrents that I have been seeding for several years. The trouble is that I can't tell whether anyone still cares about the files I am seeding. The torrents may have high ratios, but was that the result of requests a long time ago or more recently? I can't tell.
I can only seed so many torrents, so I would like the ones I seed to be the ones that people are most likely to want. If I had a column that indicated the last time that I had sent out a piece of data from a torrent, then that in combination with the "Added" and "Ratio" column would allow for an informed choice of which torrents to keep and which to delete.