I don't know...I kind of enjoy it when the librarian gives a quick, 'Oh, this book was really good' or 'I love this author'. I remember once, I was checking out a Sherlock Holmes collection, and the slightly older gentleman checking me out said, 'Quick, Watson, the game is afoot!' It tickled me so, I replied, 'Holmes, you astonish me!' and we both giggled. It was fun, just a little shared enjoyment of the stories.
Now I agree, there are things I don't want commented on, like any self help book that's on a personal level, or a history of Scrabble, or something similar, I don't really want to have a conversation, but as a general rule it wouldn't bother me if the librarian made a quick, positive comment on a book.