The USA is also the only country (I know) that force you to enter the country even if you're in transit. You have to clear customs even if you're just waiting for your connect-flight to Canada or South America.

Yup. Brought it in after 9-11. First machines were shit and didn't work. My friend followed instructions to "just press harder" until he put his thumb through the machine. Immigration chap didn't seem terribly happy but was only following instructions