Design blooper: Car park barrier
David Travis from System Concepts nicely illustrates a parking garage barrier design that gets "iterated" a number of times. He then aptly asks "how many participants would have been needed in a usability test to spot this blooper?" It's a great illustration of where usability testing would have been FAR cheaper than the resulting hacks to fix a bad design. In this example, the company who created the design is probably not the same company who bought it and was trying to fix it. Travis has also authored a new book called E-commerce Usability. Some sample chapters are available online.