It's usually good to copy the big guys. When people grow accustomed to a certain design, following it in your own interface supports transfer of learning and thus increases usability. If you're designing an application, follow the lead of Microsoft Office -- for example, use a floppy-disk icon to denote "save" (even though nobody saves to floppies any more). If you're implementing a search feature, copy Google.» Jakob Nielsen's Alertbox, July 25, 2005
For e-commerce usability, Amazon.com used to be the model. In 2001, we tested twenty e-commerce sites for usability and Amazon was the clear winner, scoring 65% higher than the average of the other nineteen sites. Having the Web's best usability served Amazon well: sales increased by 126% from 2001 to 2004.
Of course, rather than simply copy any one site, it's best to follow the hundreds of detailed research findings about e-commerce usability. But people often prefer to be told just one thing. For many years, that one thing in e-commerce design was "Do like Amazon." No more.
Amazon has recently changed so much that the average e-commerce site will reduce its usability by emulating its design too closely.
Paradoxically, Amazon's design may work well for Amazon itself. The company is simply so different from other e-commerce sites that what's good for Amazon is not good for normal sites.