I will start with what is new in KTorrent 3.1. Seeing that KDE 4 has added this shiny new library called Phonon, making it very simple to add audio and video to your application, we could not resist using it. So we have added a media player plugin, which supports audio and video. All the media files in the torrents you are downloading can be played by this new plugin inside the KTorrent application window.
Another big new feature is webseeding: we only support HTTP at the moment, but it works. You can even add your own webseed URL's, and the torrent does not have to contain webseeds itself. So you can now, for example, take the latest Ubuntu torrent, and then add the URL to the Ubuntu ISO and KTorrent will start downloading via HTTP and BitTorrent at the same time.
Alongside these big new features, there are quite a lot of smaller new features and improvements (if you want a full list, take a look at the changelog of the KTorrent 3.1 Beta 1 release).
A Windows port was started some time ago, and this is now nearing completion. The Windows port branch was recently merged back into KTorrent trunk, making KTorrent fully functional on Windows. The next release (KTorrent 3.1 Beta 2), will feature these changes.
Finally, I would like to conclude with the plans for future releases. We will further integrate the new KDE 4 technologies into KTorrent. This means Kross scripting support, a Plasma widget, and NEPOMUK will be integrated. We also have plans to dump the boring list of torrents, in favor of a more cooler looking approach using Goya. The search plugin will get support for OpenSearch, which should make adding new search engines a whole lot easier. And obviously many more features...