I am currently reading about Digital-Analog-Converters in a magazine. In one section about connecting an iPod, it says that the sound via a USB cable such as the one from Audioquests Cinnamon is significantly smoother and more velvety compared to the official USB cable from Apple.
Also, a standard USB cable: In the description of Audioquest "Coffee", they are claiming that there is a huge difference. And they cost about 280€! Or their "Diamond" version costs about 550€! Here is some review, again claiming that there is a difference. Here is another review. And here another one.
How can that be? The signals which go through the cable are digital. How can there be any difference?
(Just for reference, I also asked the same question on AVP.SE with similar answers.)