Unless I really want to be in the dark about some movie or TV show, I usually read spoilers online. I know reading about twists, shocks and game-changers beforehand only reveals plot points. The drama, human emotion, the music, et al. -- the heart of it all, in my opinion -- gets left out of the description. If anything, a great TV show or movie can stand on its own even knowing the spoilers ahead of time. This all struck me after watching this season of LOST.
My reasoning for reading LOST plot outlines is simple: due to the show starting fifteen minutes before I am home on most Thursday nights, I don't want to be in the dark when I turn the TV on. I figure it wouldn't be such a big deal if I were to find out that Kate's taking care of Aaron or Sayid's working for Ben in the future. When I saw the episodes themselves, I was really moved by the unspoken emotions found in scenes like the one with Kate and her dying mother and Sayid being fixed up by Ben. That's the stuff that surprises me more.
I think about one of my favorite M. Night Shyamalan films: The Village. The twist in that film really amazed me, but what made the movie work for me was the love story. Besides, if you're really that web-savy, you can find out pretty much any movie or show's twists and endings online. So if the foundation of something is its twist, it's not really gonna warrant repeat viewings, at least for me.
Yes, there's a lot of good in watching a show or movie not knowing what's gonna happen. I didn't read anything about Season 3's introduction of flash-forwards in the finale. When I pieced everything together by the end of the episode, I was really impressed. Probably more impressed than if I read spoilers beforehand. But that was something I really wanted to stay in the dark with. Viewing the episode again before Season 4 began (and now with last night's episode on my mind), there's even more to ponder and be amazed with. I don't blame Jack for feeling weird about Kate raising his nephew.
Now understanding this makes me realize why reading the reveal of the killer in Scream 3 didn't really ruin the movie for me. It was the movie itself.