I'm pretty new to linux, dropped windows & azureus recently, i love kubuntu & Ktorrent, but i miss some features :

1) The ability to move up and down a torrent in the queue
2) Automatic integrity check with download is finished
3) Move the file/folder when finished
4) Torrent ratings & comments : Maybe as a plugin ? Do you know if there are any doc on ktorrent plugin interface and on this rating protocol ?

For (1), the queue manager (QM) can actually move torrents up and down the queue.

Unless you mean priority?

For #2, is there any reason to doubt the integrity of a downloaded torrent, except in the case of faulty hardware?

As far as the ratings system, I believe it uses Azureus's extended messaging protocol implemented over Azureus's distributed database. This would require us to have a second DHT implementation.