I have Wireworld Chroma cables, but only because Sevenoaks threw them in when I bought a complete new system from them.
Can't say I noticed any difference when I swapped over to the freebie HDMI cables that came in the box with the Blu-Ray player and Freesat box. However the Wireworlds have better quality plugs on them that stay firmly in the socket, the freebie ones tend to fall out given a slight tug. So for that reason I'm leaving the Wireworld cables in.
All this talk of "audiophile" USB cables makes me laugh too. USB and HDMI both use a packetised protocol. The only possible way I can hypothesise that a USB or HDMI cable could make a difference to the sound or picture is if it wasn't properly shielded, was spewing out RFI like a spark transmitter, and your amplifier (or other line-level component) was also inadequately shielded and was picking up and amplifiying said RFI.
Next they'll be trying to tell us that changing your Cat5 cable makes a difference too...