I've gotten into a few internet arguments about the nature of spoilers - Tobie and I have always been very against them. There's no real point in revealing spoilers online other than to feel a false sense of entitlement for knowing something before someone else and trying to rub it into their faces. There are better ways to discuss the nuances of any story, may it be a movie, TV show or book. Shouting your spoilerly opinions in a public status message is hardly the most ideal discussion ground.
A popular argument in defense of some spoilers - at least those for works adapted from books - is that people should have read the source material before getting into the TV show or movie. The logic here is that since the source material exists, there's no excuse to claim to have been spoiled by a book-based revelation. But that's horrible logic - the mere existence of a story does not mean that everyone has the means or the desire to read it. And if we were to follow this same logic, then any movie or TV cannot be spoiled the moment it has been released to the public. Both arguments rely on the fact that the existence of a thing means that it is accessible and thus the burden of knowledge lies on the shoulders of the individual viewer or whatever.
In a weird turn of events, the internet is somewhat afire regarding a particular scene in this week's "Oathkeeper" episode of Game of Thrones. The assertion is that it appears the TV show has potentially spoiled an unrevealed fact that has not been established in the books thus far. But it may be a little hard to argue how true this statement is since, well, it hasn't appeared in the books. The one thing that makes all adapted works rather unique is the fact that they often take liberties with the source material. And thus each version of a story as it goes from book to movie to TV series to comic book, and so on, each often tries to innovate somewhat in order to better tailor the story for the target medium. But of course the author, George R.R. Martin, is heavily involved in the writing of the show, so it seems pretty clear that there's some water to be found here if you're thirsty enough.
For me, spoilers are more about how much you care about other people who are experiencing a story that you may already love. Not giving away spoilers means that you want the other person to experience what you experienced when you first turned the page and discovered that pivotal detail that turns a story on its head. Keeping spoilers to yourself means that you want to be able to talk about the experience of the revelation with the person after the fact and thus have something else to tie you together as friends.
Giving away spoilers just shows you're a dick, a douche bag who wants to appear somehow smarter about something. But in the end you're not smart at all - someone will always know some intimate detail of a story you've yet to experience and one day they'll spoil you because you deserve it.
Help your friends get the most out of any geeky experience - let them experience a story, whether a book, a movie, a TV series, a play, or a comic book, with the open mind of someone who knows nothing. You'll be all the better for it in the end, I guarantee.