One by one, US ports of entry are introducing "automated passport control" for holders of US and Canadian passports. More details and lots of opinions in this FT thread.

In a nutshell, more and more people (US and Canadian citizens plus people who've paid for Global Entry and related programmes) are getting to go through the first stages of entering the country without being questioned by a human. They scan their passports, answer questions via a screen and get 'receipts' from the machines. They then need to hand over the receipts and show their passports when exiting the customs area -- at which point they may be asked one or more questions.

A side effect is that permanent residents now have to queue with visitors.