It's a real bitch if they tip over and get intermixed. I had a shoebox full of cards for one of my freshman CS projects in college that got spilled on the floor, it took me a couple of hours to get those ~1000 cards sorted in the right order. After that I drew a diagonal line across the top of all of them so sorting would be much easier if it happened again. Cards sucked. One line of code per card. Datasets could have multiple values on each card.