How much are easy-to-consume, intuitive user interfaces worth to companies today? On the list of "must haves" for CIOs, tech pros and non-IT executives involved in large software development projects, quality user-interface design probably doesn't even show up on RFPs or in-house development plans. With TCO calculations, installation timelines, integration and architecture scenarios, and security and customization concerns to determine, user interface design quickly falls by the wayside. (Indeed, it's nowhere to be found in a new Forrester survey report about the benefits and drawbacks of SaaS.) Those software development priorities are probably going to change at Zappos.com. The online shoe-tailer recently fessed up to a $1.6 million loss at its sister site, 6pm.com, due to a pricing error caused by overly complex business software. The result? Shoes that were priced way too low. Zappos.com CEO Tony Hsieh explained the situation: We have a pricing engine that runs and sets prices according to the rules it is given by business owners. Unfortunately, the way to input new rules into the current version of our pricing engine requires near-programmer skills to manipulate, and a few symbols were missed in the coding of a new rule, which resulted in items that were sold exclusively on 6pm.com to have a maximum price of $49.95.A $1.6 million loss certainly gives new meaning to the word "glitch."Zappos.com isn't the only company to have experienced pricing errors: Amazon.com's $3 billion CD-ROM error and Best Buy's $9.99 52-inch flat-screen TV mistake are two other examples of online pricing mix-ups. In Zappos.com's case, a difficult UI combined with an inefficient process equaled a destructive business outcome. (Ironically, Zappos is no tech laggard. Have a look at the robots at work in its warehouse.) Why do companies continue to make these design mistakes? Too many IT staffers get so hung up on the back-end stuff, they sometimes forget the users. "What is a good interface for computer engineers is not a good interface for the average person," Web-design guru Jakob Nielsen told The Guardian. "A lot of computer guys don't recognize that, and it creates problems." The basic, first-move question should always be: "Who are the users and what are they trying to do?" Nielsen asks. Great advice. I bet Zappos.com's Tony Hsieh and his IT leadership have been thinking about that a lot lately. Do you Tweet? Follow me on Twitter @twailgum. Follow everything from CIO.com on Twitter @CIOonline.