MtGox emailed me a free Yubikey coupon code. I sold it to someone. But MtGox ended up shipping the Yubikey to my address, tied to my MtGox account. MtGox Support confirmed that coupons are tied to the account they are first offered with.
I have no explanation for that then. Although my buyer encountered bugs on MtGox's website and we had to ask Support for a sort of reset URL to re-activate the coupon code. It is possible my experience is somewhat unique.
It's unique for you. I got a free yubikey from Mt.Gox, ordered it and it arrived to my courier address at the US instead of my AML verified home address in Venezuela. If I send it directly the thugs from the postal service will steal it.