For me it depends on the subject. Sometimes I will set out to make sure I don't have any spoilers at all, and sometimes I will read as much about it as possible, getting as many spoilers as I can.
For example, I'm currently reading A Game of Thrones, and a friend of mine has spoiled a few things, but I'm not too bothered as I'll still read and enjoy the book. On the other hand, when the next Pokémon generation comes out, I want to know as little as possible.
So what are your opinions? Do you think spoilers take away from the experience? Or do you make sure to read the last page of the book, because you can't help yourself?