Mt. Gox shall not replace any key lost by a Member.
So what happens if you lose one?
You pay them for another one, I guess. This to me reads like "if you lose it, we're not paying to replace it".
If only it were that simple. You see they replaced mine at no cost to me, then said they couldn't send one at all. One way or another, they did not follow their terms of services, but instead made stuff up as they went along.
Thank you for contacting us. Please be aware that in cases of a lost Yubikey, we can only resend a new Yubikey to the same address as before due to security reasons. We will request our management group to unlink your Yubikey from your account. Unfortunately, we can not issue a refund since you did not pay for the replacement Yubikey which was complimentary from us.
First they told me they'd send it to a new address, it gets refused at my old address, then they wont send it back again to the old address.
My point is it's really not safe to assume MtGox's inconsistencies in services and policies will work out in your favor.