It work up to 20m if you use good quality USB cable and a little hack.
First USB cable have only 4 insulated cable under the shield, so i combined the shield and the ground of the split Kinect cable and connected it to the shield only of the usb cable. Then i used the USB cable black wire to connect the Kinect extra yellow cable. All other color should be matching.
KINEX Cable; USB Cable; Description;
Shield + Black; Shield; Gnd
Yellow; Black; +12v
Red; Red; +5v
White; White; Data-
Green; Green; Data+
I also tried to add a dual connector usb and kinect at the end of the modified kinect cable but this didn't work although i am sure it would have worked without the usb extension part.
Of course an active USB repeater cable would be better but that was a quick fix as i couldn't find the official M$ extention cable in store and couldn't wait for it to ship on-line...