i use the library a lot for books i will only read once or a few times (yes, i have and do check out the same book more than once from the library, like after a year or two has passed since reading it ), especially for interloaning books.
i also buy books, from my favorite authors, which i will read and re-read (i've re-read 'Mossflower' at least 9 times and still enjoy it each time i read it). or my Christian apologetics books, which i have a fair collection of, especially CS Lewis (i have at least 24 of his books). some books i use as reference. but i'm always buying more books whenever i have money to be able to. i also buy a lot of manga, which i tend to re-read a lot as well.
i have a lot of books, and brought a good deal of them to college with me... i have two bookshelves at college, as well as another bookshelf at home, all full or pretty close to full.
i also plan to keep most of my textbooks from college, since i'm an architecture major, it's always necessary to have books to flip through to get ideas and inspiration; and i will need to keep the *fun* books on building construction and codes and stuff like that.