Which is the exact opposite of how I feel about it. Because there are movies I still haven't seen fronm the 1950s, where discussion of the twist in the tale would spoil the movie for me. And I'm very aware that the majority of people who go to see the new HP movie won't have read the book.
To me, spoilers are all about politeness. If you tell someone the end/twist of something they didn't know, and will possibly experience in the future, when they didn't want to know, then you've spoiled that experience for them. I remember the feeling of watching Empire Strikes Back and discovering that Han and Chewied were lovers. The shock and surprise at the moment of reveal was an integral part of the experience for me, and taking it away from people that haven't seen the movie yet is just plain rude.
Now, you can argue that it being years old, the chances that people on your friends list haven't seen Empire Strikes Back is low. Which is true if you're posting friends-only and have nobody under the age of 20 on your friends list. But it's not like the olden days, when a movie would appear, and then vanish again, when TV that had made the rounds was lost. Nowadays I can go out and buy box sets for TV made before I was born, and watch it entirely fresh. There are more hours of TV and movies out there than I have time to watch in my whole life, and the chances are that some will be watched years out of synch with their original release. And I'd really appreciate you not telling me the details before I do!
Obviously I consider all of the following to be spoilers. I'm curious whether you do too. If you don't then I'd love to know why...
I would consider the following to be spoilers
The end of Battlestar Galactica (2009)
The end of season 2 of Battlestar Galactica (2007)
The end of Harry Potter and the Half Blood Prince (2005)
The end of season 2 of Babylon 5 (1996)
The end of The Empire Strikes Back (1980)
The identity of "Rosebud" (1941)
The end of Hamlet (1600)
Also: NO SPOILERS IN THE COMMENTS!