I have never sat down and prepared a chapter outline before writing a novel. I tend to write my way into a piece, usually with an idea of the ending and of the basic structure (all three of my Undine books have a central shift, that changes the direction of the narrative and I always know from the outset what this shift will be) but I make up the rest as I go. It's not necessarily an efficient way to write, Breathe and Drift both went in very different directions at first and I had to do a lot of deleting. I think it is quite an organic process which leads to quite satisfying character development and in a way it's kind of a chaotic system because one line when I'm writing, one observation or image, can lead to a whole subplot or affect the character's destiny, much like those butterfly wings in Japan.
I found this, which is a very interesting article about how Australian fantasy writer Garth Nix plans and writes his novels (in longhand!!). I have a vague idea for a fantasy trilogy (yes, i know, I am sure I swore I would NEVER write a trilogy again), which I can't start for a year or two because of other obligations. So I was thinking I might try keeping a visual diary for it, jotting down thoughts but also sticking in images to help give shape to my vagueness. Will let you know how it goes.
And I am writing a chapter outline now for a chick lit novel I might be writing for A&U. It's interesting solving all the plot problems at this stage! I am actually writing it in first person, it's the only way I could get the story to come alive. So if the chapter outline is accepted and I proceed with the book, I'll let you all know if the outline made it easier to write and if I think the loss of spontaneity affects the writing process (I'm deeply curious to know myself!)