In a stroke of pure genius, Ken Arnold introduces his "napkin look and feel". The purpose behind it is to keep stakeholders reviewing the design from considering it "done". I think this has two dimensions: 1) it makes it seem easier to change, and 2) it doesn't look as though it can be shipped.

If only we were developing a Swing app at my shop, we'd definitely be using this technique. Instead, we build static HTML prototypes that our UI guy always polishes to perfection (even though I've repeatedly mentioned that we should not try to make it look to pretty). Maybe we should attach an "ugly" stylesheet to the prototype, although we could never get the same great hand-drawn effect.