I almost got one on two occasions at SFO -- two weeks ago they had one available, but wanted a $25/day upgrade fee over my C reservation, which was a bit too much for me (the agent said it was in H).

At the end of last week, they had another one sitting in a stall that was open, but it was reserved for a Platinum.

From what I could gather, it's actually a YC and still in "trial" mode, so you can't really request one until you get to the airport (at least at SFO).