It is a little embarrasing to talk about books when I have not read nearly as much as I would have liked to in the past dozen of years. Nothing can more readily showcase my paucity of knowledge than the empty bookshelf! But what is a(n)(e)house without a(n) (e)bookshelf?!
Fields of interest--I occasionally check out books in a particular field. Since I know even less on these topic, usually it is the first book that holds the special position in my mind.
Unreadables--I almost always finish the book I've started, even if I don't like it. Sometimes a book can be so bad or incomprehensible that I have to walk away halfway through. Occasionally I would still be upset whenever something reminds me of it (like preparing this page). So these books get to hold a "special" place here while hundreds of others simply fade away.