In James Scott Bell's book Plot & Structure, he has a test in the appendix to find out which type of writer you are. There are advantages and disadvantages to both. If you plot out your whole novel you are less likely to leave any loose ends. On the other hand, to let your story and characters take you where they will is very nourishing to the creative mind.
Me? I'm actually a little bit of both. With my first novel, I had a chapter by chapter outline. My second novel, I used what I like to call a "plot-line". I laid out a long piece of paper horizontally, and put in major points and events. Somehow, the characters always made it there, and even surprised me along the way. With my current work in progress, I am letting the story unfold as it will. I have a general idea where it's going, but even I am surprised by what is happening.
How about you fellow writers?