Mt.Gox Yubikeys are linked only to the user's original account. We cannot unlink the Yubikey from one Mt.Gox account and relink it to another Mt.Gox account. If you wish to purchase a Mt.Gox Yubikey for your own account, please order one from our website at
https://yubikey.mtgox.com/.
Yeah I probably wouldn't pay more than 1BTC for a used MtGox Yubikey, which I would then reprogram for some other purpose since it's useless for MtGox.