I use index cards for EVERYTHING. I wear a large jacket, with eight pockets, plus my pants pockets, and my over-shirt pocket, making it a total of thirteen. Three of those are currently occupied by stacks of index cards. I never use them for actual writings of stories. But I will constantly use them for programming, game design, language-learning (esp. Japanese Kanji), to-do lists, line-learning for plays, and straight-out notes. I have one stack of them that has a large supply of writing exercises. I order them in masses, five packs of a hundred each at a time.
Sorry, I got a little caught up in my excitement over the subject. In short, yes, I do use index cards.
-giusti