I found this earlier relating to repeat ESTA visitors:
U.S. and Canadian passport holders and international visitors from Visa Waiver Program countries are eligible to use APC kiosks. Visa Waiver Program visitors must have Electronic System for Travel Authorizations (ESTA) approval prior to travel and have visited the United States on at least one occasion after 2008.
I didn't know this. So I could use the APC kiosks if I wanted to, but from some of the comments above, it might not be any faster?