Spirals show up everywhere from fractals to nautilus shells. Software developers know the spiral as iterative development–a model in stark (positive) contrast to the old linear waterfall model.
One huge problem with the waterfall model is that in its traditional form, it’s not based in reality. It assumes that it’s entirely possible for each stage to be done perfectly (and permanently) and then thrown over the fence (or cubicle wall) to the next group in the system. Nice theory, that. The guys doing the requirements finish their job and then, hey, they might as well all go on vacation. Their work is done. And so on down the line until the product is delivered to the users. The name itself (waterfall) describes the key limiting characteristic of the waterfall model–it’s one way only. Water doesn’t go back up.
User experience designers (especially with games) often use a spiral model to keep cycling the user through stages of interest/motivation, engagement, and payoff (I described the user experience spiral headrush.typepad.com…