Looks like the following site is the best place to keep track of keys they are handing out ... not just this batch, but I suspect it will clear itself out and update the next time they hand out keys as well.
ADDITIONALLY, unbeknown to me (obviously) they are handing out keys NOT just on Twitter, but also on Facebook.
Don't have either kind of account .... me fuckin' neither .... but you'll see on this site they will list both, and the codes are, in fact, different ... more keys!
Lastly, the first three listed also will give you a key one time (like all other codes), but I just entered everything listed there and got keys for every damn thing .... sure, a lot of excitement over nothing, but all I've got is nothing so I just toss it on the pile.
Anyway, the aforementioned url:
http://orcz.com/Borderlands_2:_Golden_Key?all_keys