I've spoiled stuff before, but only at the request of others, and even then I try not to reveal the truly key points or elaborate too much on it. I'll start using the Black Glow Spoilers, which should be easy for me to remember as it's acronym is BGS, a grading type in Magic The Gathering.
I also support Magoo, and say that we should have punishments for spoiling. It must be driven through that ruining other things for people is NOT okay, even if one person asks for it If that last bit I said makes me accountable for my own errs, then I accept any punishment given to me. However, I do believe that this should not be done retroactively, but from this point forward. Also, in my own opinion, it should not be voted on by the people, as many people here spoil, and would inherently vote against it. I do believe that it should happen, but only after deliberation by the moderators, to decide if such a decision would positively affect us.
Adding to that, if someone does want to know just PM instead of spoiling it for all the other people that may see it.