"As more and more MP3 player makers improve their devices' external design, the user interface is becoming an important differentiating factor, the chief executive officer of one of the world's biggest MP3 player makers said Wednesday. Joon Yang, CEO of South Korea's Reigncom, which produces players under the IRiver brand name, said that the exterior design of his company's devices used to make them stand out from the competition. But competitors have caught up on exterior design, pushing IRiver to focus on something else."Better late then never I suppose. I've only used a couple of IRiver devices, but the ones I've used had the worst user interfaces I've ever seen, so much so that when I think of bad UI on MP3 players, IRiver is the first company that comes to mind.