As usual, when something is released for free people just gather as many keys as they can without even knowing what to do with them.
I happen to know one of those guys, and since he took several keys for Metro 2033
from Humble Bundle he gave me two, saying I could do what I please with them. Anyone interested?
Just reply to this message, and I *might* give you one! ;)
EDIT: My friend Enebias got confused, I was just joking, not really making a claim. :-)