If I go to View->Threads I can select to view only watched threads, or to display ignored threads.
How do I set this on a thread? I keep searching, but there just doesn't seem to be any option to mark a thread watched/ignored.
You can only watch/Ignore News threads, not ordinary email, or RSS feeds.
When viewing a news message, these options are under the "Message" menu. "Ignore Thread" (K) and "Watch Thread" (W) are at the end of the menu.