There are threads of a controversial nature which one finds difficult to ignore even though one wants to ignore them - they tempt one to get involved in what is usually an argument even though one knows that the outcome will not be pleasant.
Would it be possible to have a feature similar to ignoring a user, but with the difference that the thread really is invisible?
Ignore user allows one to see that the user has made a post, but one can't read the post.
When ignoring a thread, however, one does not want to see any activity at all - it is the very activity which tempts one to have a "peek".
Such a feature also would allow one to keep the list of threads that one sees "tidy" - hiding threads which cover subjects which are outside one's scope etc so that one can concentrate better on the others. This is especially important when using cross-forum facilities such as looking at the new/latest posts.