I purchased four windows 8 keys during the buy a laptop now upgrade to windows 8 promotion.
I have been sitting on these for quite some time, used only one of five since launch.
Yes you can use a windows 8 iso and use this key to activate no problem.
PM if you want one I will send you BTC Addy.
Send me your pgp key to pm the win8 key back, unless you don't care.

$25 each BTC.

from my 10-26-12 notifications "Congratulations! Here’s your Windows Upgrade Offer promo code for Windows 8 Pro. Purchase and download your upgrade now." I purchased using this promo just never used them because... well... it's windows 8.