I came across a recent post on Nabokov's Index Cards by Michael Leddy, which I found interesting.
Nabokov wrote with Index Cards not so much because they allowed associative progression (or because they were somehow like precursors of hypertext for him), but rather because he had such a clear vision of what he meant to create that he could start anywhere in describing it: "The pattern of the thing precedes the thing. I fill in the gaps of the crossword at any spot I happen to choose. These bits I write on index cards until the novel is done. My schedule is flexible but I am rather particular about my instruments: lined Bristol cards and well-sharpened, not too hard, pencils capped with erasers."
"... Since this entire structure, dimly illumined in one's mind, can be compared to a painting, and since you do not have to work gradually from left to right for its proper perception, I may direct my flashlight at any part or particle of the picture when setting it down in writing. I do not begin my novel at the beginning I do not reach chapter three before I reach chapter four... This is why I like writing my stories and novels on index cards, numbering them later when the whole set is complete. Every card is rewritten many times ..."
"find a quiet spot (pace the booming surf and rattling wind) where to write. This I do on scrambled index cards (my text existing already there in invisible lead) which I gradually fill in and sort out, using up in the process more pencil sharpeners than pencils; but I have spoken of this in several earlier questionnaires"