Bruce 'Tog' Tognozzini writes When Good Design is => a Bad Product.

You take a mediocre product and rework the design to make it better. Your design is a success, by any reasonable measure, but the resulting new release is actually worse. You redouble your efforts and matters become untenable. It doesnít matter how brilliant and effective your designs, the more they improve the product, the less usable the product becomes.

The article is filled with wonderful illustrations that will help us better understand how to make better products.