Democrary Player (to be renamed Miro) has a nice shiny interface, but the playback's terrible (even though it apparently uses VLC or xine) and the video's always full-screen and blocky.
PenguinTV, on the other hand, is very nice. Written in Python, minimal and small (using external libraries for feed parsing, BitTorrent, search indexing, etc), it does the job well.
What do these do? You give them feeds (eg those from tvrss, filtered by release group to avoid duplicates), each new episode is downloaded (either manually or automatically) and then you watch them.
See also: ted, which watches feeds then uses your preferred BitTorrent client to download the actual files.
I've retired torrentbot, partly because there's no working jabber server for Ubuntu but mostly because these new applications do the same thing much easier (though it would still be nice if they sent you an IM asking if you wanted to download a new episode).