I kinda told one of my friends who watch the series "a few" things about the book. He kinda likes the Others, so I told him the we will see them in the third series.
"A few" means kinda a lot but I haven't told him anything about Oberyn, the Krakens, the Red Wedding (he knows Rob will die, but doesn't know how), the Iron Throne (he know something but not much), Arya, Sansa, Davos, Jaime, Cersei. I told him something about Dany, but not much and some things about the dragons, Jon, Bran.
it was a 2-3h talk about the series and books, also in order not to spoil much I kept several thing from him.
Anyway, he still likes the series and will keep with it. Funny thing is, I told him about the books and that a series will be made, and tuesday, after the first episode, we meet and he told me he watched the first episode.