Never had Customs scan and look at my passport anywhere - Europe, USA or Asia. Not once.
However, Immigration always scan and read my passport
I have been secondaried by Customs 4 times. 3 at LAX and 1 at IAH. In all of those cases they scanned my passport and spent an inordinate amount of time looking at the computer. Often followed by comments about my travel patterns. One time at LAX the Customs agent also made a comment showing more detailed specific knowledge of the IAH secondary beyond just that it happened. The IAH secondary was uneventful and found nothing but the LAX agents made some benign comments that led me to believe he read a somewhat detailed report of the IAH search on his computer.