We’re thinking more about this now that our API is nearing.
In the meantime, note that you can block any member from following you or posting comments on your content (look for the Flag icon on the member’s page).Sam commented
I too would like this. There are some films I want to track but not publicly mention. It's not like facebook where only your friends (or at the very least people who are logged in) can see, everybody can see letterboxd ratings.