There was a study awhile ago that showed that people who knew the ending enjoyed the book/movie/video game more because they could appreciate the intricacies more. Instead of focusing on what's going to happen on the end, you can focus more on the small things. The best example of this is Oedipus Rex. Everyone knows the story. Oedipus can't escape fate, kills his father, and then marries his mother. Sophocles' tale of this revelation is that much more interesting due to the dramatic irony - we all know the truth, but they don't. It's a really interesting way to tell a story.
To answer your question, I personally do. If I know the ending, then I pick up on smaller things, subtle foreshadowing, and things of that nature. It's actually a really nice way to read a book/watch a movie/play a video game. I actually rewatch/reread/replay these things in order to achieve a similar effect, but already knowing the ending quickens the process. So when I experience that media a second or third time, I can experience it in an even more thorough light. It's an unorthodox way to do things, but I particularly enjoy it.
There are only a few instances in which I don't particularly appreciate having something spoiled for me. If it's a video game I particularly like - Bioshock, namely - I don't want it spoiled for me. For some reason, I like learning the plot twists firsthand so I can't allow someone to spoil that for me.