A forthcoming study from two University of California, San Diego academics supports what I've thought for a long time: knowing whodunit in a mystery or thriller doesn't necessarily ruin the experience. I think it explains why some people (like me) re-read mysteries (and no, it's not because I can't remember the endings). Nicholas Christenfeld, one of the study's co-authors (I really like the presentation of his publications here), says the research explains why people actually enjoy knowing the ending. I understand that. They can concentrate on the journey along the way rather than obsess over the problem of the perpetrator.
But some people don't agree. They like the mystery, and that's understandable as well. They like puzzles. That's why they read crime novels, and watch thrillers. This research by Dr. Christenfeld and his co-author Dr. Jonathan Leavitt might also explain part of the debate in magic circles over exposure. Some practitioners say it ruins the performance for the audience, and condemn those magicians (like Penn & Teller) who make a practice of explaining at least some illusions to their audiences. But some magicians say knowing how a magician performs an illusion doesn't really matter. A magician can still amaze with a performance.