There is another way to find the serial of your console,and it is by looking at a sticker under the metal shrouding that holds the motherboard.I can confirm this method works as I have checked two consoles by using this technique and they both match the case serial number.You can also use a made up serial like the tut,but finding the original serial isn't hard either.
haha, i took me a while to find that one when i was sending a 'defective' console back to MS a while back. i new the one on the back so just switched top halves of the case, new the one on the 'bottom' of the mobo shield and found the USB one when i was putting the front plate back on, i was like well damn these people and all their SN stickers, one is enough.