I am a big advocate of Paper Prototyping although it seems the opportunities to use the methodology are few and far between. The traditional arguements against it are that it adds cost and time to the planning stage of a projects. Because of that, it can be seen as an expensive exercise, even though it eventually saves money and time on the flipside of the project during the development stage. It is also perceived as more closely tied to the traditional waterfall effect because of how much work is required before you can start coding and building with the computer. In the arguements of what is waterfall and what is agile, I would argue that Paper Prototyping is the most agile of processes because it solves so many issues up front in the planning stage, is highly iterative, and involves the team in a highly colaborative exercise. Joel On Software had an article a few years ago praising this methodology. So the question is, “Is Paper Prototyping considered part of software development, or something you do before you start developing software?”