I have extended all my cables and things are fine. For USB I added a mini usb hub (self powered) to the middle console and then ran the cable from the trunk to that. Then I could branch out to whatever else I add to the dash area.
Once you go too long though, USB needs a power boost - might want to check into thel imits of the extension cable length. I had no probs tho. And my vid signal extended all the way up to the dash from the trunk without problems or loss of signal.