Taking Tracy's class on designing for interactive media has opened my eyes to the wonders of paper prototyping. The great thing about paper prototyping is that it can be used for not just games, but for software too. Apparently someone at Adobe must be in contact with Tracy because if you check out the link below you will discover what could potentially be the greatest paper prototype of them all.
http://gizmodo.com/5080163/what-photoshop-would-look-like-in-real-life