I'm actually very bad about spoiling stuff for other people- gotta work on that.
Sometimes I actively try to avoid them, but usually my curiosity wins out. I do use spoilers as a measuring stick of sorts, though: If I find some spoilers and that makes me stop watching/reading, it prolly wasn't that good anyways; but if I catch wind of the ending of something that's very well done (FMA is a good and recent example) it makes me even more excited to watch and see how the story developed to that point.