Oh wow, we finally ran out of keys when I wasn't looking! I've requested more from Steam and should be able to restock the supply in the back end soon. So more keys are coming, and you'll be able to redeem yours soon (hopefully no later than Monday, but if Valve is quick then I'll restock the keys before that). Sorry about the wait on a response, I've been hellishly busy for the last little while.
Edit: Valve was on the ball today, the keys have been restocked! Sorry for the wait.