I just tried the code for xbox and it doesnt work. Kind of pissed off cause these codes don't run out.
Are you inputting it through the game's main menu? If so, sorry to hear it didn't last long. This site hasn't removed it, yet (http://orcz.com/Borderlands_2:_Golden_Key), and it seems to stay on top of things.
Also, two other codes were issued yesterday (see site), and they appear still valid.