I haven't read the books, but I frequent the Game of Thrones wikia, where every episode has a section titled "In The Books". Not being able to help myself, I always read this and often regret it, because it reveals many things that haven't happened yet or were supposed to happen already but will. It often reveals/spoils deaths of major characters. I always kick myself for reading these "spoilers", yet I can't help myself and read these "In The Books" sections when every new episode airs. I know a lot more about what happens in the future than the average GOT-viewer-that-hasn't-read-the-books because I can't seem to stay away from that damn wikia page.
Having said that, I don't like spoilers here and appreciate when book-readers put in the very minimal effort to use spoiler font. I like joining in the GOT discussion, as much as I can, as a non-book reader. I do have all the books and will read them eventually (read the first one) but I'd prefer to be surprised on the show, then read about it.