As a tag along to the subject matter.......
I came through JFK T.4 yesterday and on the gate at 15.35.
Followed the usual signs until a split came between signs for first time ESTA arrivals and returning ESTAs. As a returning ESTA member I was directed to a machine, fingerprinted and photographed by the machine, process complete and into baggage hall withing fifteen minutes of gate arrival. All staff at JFK were extremely helpful and patient.
I will admit that our arrival caught a gap between the 13.00 and 16.00 rush but the experience was worth leaving the US for in order to do it again. We were in the train on the way to Federal Circle 1/2 after arriving at the gate.
The significance of course is that there is now a distinction as between a first time ESTA and any other one.