In today's Star Tribune, people wrote in to complain about writers, TV, and people in general ruining the ending of books and movies and such. For something like Harry Potter, you really can't avoid hearing about things. This is usually why most people go out right away and read the books...otherwise you learn aspects that you don't want to know.
I personally don't see this as a problem. Maybe it's because as a reader, I'm not goal-oriented, but process-oriented. Let me explain:
1. Goal. Ok, when you read, you have the goal of getting to the ending. For example: you read a murder-mystery, and all you want is the name of the killer. You also want to see what happens to the killer.
2. Process. You want to see how the detective/hero/heroine solves the crime. You want to see if you can piece the clues together before they do. For example, in one current extremely popular novel (ok, DaVinci Code), all the clues for who the bad guy is are in the text. If you read the book looking for them, they pop out. If you just read to get to the end (and the identity), then you miss the subtle clues.
Film does the same thing. One of the most famous films that people either go for the process or go for the goal is The Usual Suspects. Is you just want to know who Kaiser Soyze is, or you try to figure it out before Agent Kujan.
At the same time, many people hate the process people. Why? We're the ones who, during a poorly written mystery, figure out everything quickly and say, with oh...an hour left, it's this person.
The angriest I ever saw a goal-oriented person was at my wife's company Christmas party last year. They went to the The Mystery Cafe and watched a dinner theatre show (and quality) about a boss being murdered. Sadly, I knew what was going on by the appetizer. When someone asked me, I told them my opinion and thoughts. It turned out I was right...and she was pissed.
There are other ways, however, people get to the answers they want. When my father, for example, gets a book that he just wants to get to the point of, he reads the first 40 pages and the last 40 pages. "Everything," he tells me all the time, "is answered in those 80 pages. It doesn't matter how long the book is. The first and last 40 pages."
Some books and some movies, however, no shun this idea. Occasionally an author or film maker gives the audience the ending and then the rest of the novel or film is piecing together how that happened (I like those stories). Examples? Memento is a great one.
I understand that it's really frustrating when someone gives away the ending, but look at this way. If you know what's going to happen (or in certain think you know what's going to happen), then start looking at how the author or director (or writer) is guiding everything toward that ending. Are their clues or signs? Does someone or something foreshadow? Make it interesting. I'm sorry if so many people are upset by learning the ending of the new Harry Potter book, but start looking now to see if there are clues.
Have a great day.