Mt Gox codes are exactly that - a promise of actual BTC. As long as Mt. Gox keeps exactly the number of BTC on account that they have promised in all of their outstanding unclaimed codes all is well with the world - peace, harmony and love. However, if people start using the codes themselves as a longer term store of value or worse yet as a medium of exchange then Mt. Gox may be tempted into issuing more codes than they have BTC and the evil dark lord of fractional reserve banking will rise again
As consumers we can prevent this by using the Mt. Gox codes for only a short period of time and claiming them as soon as possible. Also ony accept actual BTC as payment (coins ok as they contain actual BTC) - never accept promises of BTC for payment.
There is already a market for the codes. You can buy them with credit card payment at http://www.mrcoins.org
Sorry to bring up an earlier post, but I thought I'd address this point for clarity's sake. Mt.Gox Redeemable Codes for either bitcoins or traditional currency automatically "remove" the relevant sum from a user's account on their creation. These funds are then held in limbo until the code is redeemed. As such, it is impossible for a user to create a redeemable code for more funds than they have access to.
Since these funds are drawn from a user's account, a redeemable code represents funds which are in existence at the time of its creation, which are held for as long as it takes for the code to be redeemed. Since the actual amount
of bitcoins or dollars won't vary in a user's account over time (unlike the value
of those funds) then as long as an entity which accepts Mt.Gox Redeemable Codes exists, they will be valid.
Of course, this assumes that Mt.Gox does not access, use or alter user's funds in any way (apart from the taking of trade fees), but I hope the community is willing to trust us on that point.
If there are any other questions or concerns in relation to Mt.Gox Redeemable Codes, feel free to contact us on the forums, or at firstname.lastname@example.org