I opened the Golden Chest in Sanctuary with the Golden Key I got with my pre-order bonus. I noticed that it ate my key, threw some loot at me, and then the chest didn't go away. I tried to open it again and it said I couldn't "afford" it and then displayed that I have no more Golden keys, which leads me to believe you can get more of them. If I can, how do I go about doing so?
To get another Golden Key you can register at http://shift.gearboxsoftware.com and create a new character. Then select your old character and enter the shift code you were emailed from linking your email and Steam account to SHiFT.
Also, be sure to follow Gearbox Software on Facebook and Twitter. According to Randy Pitchford, President of Gearbox, they plan on doing code SHiFT code giveaways to add more Golden Keys via these official sources in the future. (source) They have several keys a week so far, usually a couple each day on Saturday/Sunday. They're still testing the concept according to Pitchford, so they may change how they do things.
As of October 2nd, 2012, Duval is still sending out SHiFT codes on his Twitter in an effort to test out the software that will eventually be used for the giveaways. Since he is just testing the software, this could stop at anytime though.
UPDATE: The developer has patched this so that this Golden Key hack does not work on the PC anymore. The console hack does still... so far.
If you're on the PC you can go to directory of the game then go to DLC, then premium club, then open the
WillowDLC.ini with Notepad and edit it to:
[GoldenKeys] +SourceId=254 +NumKeys=300 [PromotionalUnlocks] +UnlockId=2
this will give you around 260 keys to use at your will
For Xbox 360 and PS3 watch this video for unlimited keys
On the PC version of Borderlands 2 your save data is broken into two parts: profile and character save. The profile contains shared information between your characters such as bad-ass achievements, skin unlocks, and the golden keys.
Your character save contains weapon load-outs, current location, and class tree info. Try deleting your profile and starting a new game with a new character. This should give you a new key. Then import your old character save into the new profile to access the key. Note: You will lose all information attached to your current profile if you delete it so back it up first.
This work around can also be used to unlock the chest as many times as you like. Also, your save data should be located in: documents/mygames/borderlands2/willowgame/savedata for those who don't know.