Lest I be caught in the past, I have played some modern games on my modern PC. So while I was signing up for the Borderlands 2 Loot Hunt, I noticed that by linking that SHiFT account with my Steam account, I suddenly got another Golden Key. Yesterday, I was digging around to find out when (as in, what level) is the best time to use a key.
In so doing, I uncovered a motherlode of keys. Apparently, Gearbox frequently gives SHiFT codes away that adds Golden Keys to your character. Many of them still work! Last week, I had one Golden Key. Now, I have 70! If you play Borderlands 2, I recommend you get these right now before they are all gone!
Edit (2020): Subsequent Borderlands games also have golden keys, so here's the list of current links: