usb cables can make a difference but it will depend on your system as to weather you will hear an audible difference, saying that a cheap £1 cable is not going to be as good as a well built £50 cable and anyone who says it will is quite frankly wrong,
i have tested several usb cables in different price catagories and the biggest audible difference was cables ranging from £1-£50, this is were i heard the biggest difference, i tried a belkin usb cable from poundland against a chord usb cable and immiediatly threw the £1 cable in the bin, utter rubbish.
saying that i have tested the same chord usb cable against a £400 tellurium q usb cable and although there was a very slight difference i wouldnt pay an additional £350 for it.
in conclusion i would say a well built usb cable is all you need, there is no need to pay mega bucks but on the same note i wouldnt scrimp and pay peanuts.
i know alot of people are set in there ways and will want scientific proof, to those people i would say just try it, if your happy with your 1 pound special from world of quid then good for you, but you wont be getting the best from your system.
here come the fireworks..... im off.