The Meyer-Briggs test for personality type is making the rounds on several lists. My results were, predictably, INFJ. Even after answering in my most social mood, my results are 89% introverted. That sounds worse that it is. Here are different profiles of the INFJ type. I'd bet that most readers and book lovers fall into this category although with various per centages.
Take the test and let me know where you fall. I'm nosy. And I do bet that the majority of you are introverted to some degree. :)