Ultimately it depends on the book as I could probably be almost any of those types at one time or another. I tend towards keeping and re-reading favourites, but some books I'll read once (or only partially!) and give to charity or will borrow from the library/friends and never read again and others I'll borrow to read and then buy my own copy.
My copies of the Terry Pratchett books and Tolkien are VERY well worn after many readings, some of the discworld books I've probably read 5, 6 or more times and are a great comfort when feeling down. I limit my book storage space though so tend to have regular clear outs to the local charity shops so that I don't get overrun with books... I have too many shelves full of dvds and blu-rays as it is!
