If you've been to the US recently, you'll have encountered US-VISIT. This is the charming system that takes your photograph and fingerprints at immigration, although I've never understood what this will tell them that my passport - and associated gigabytes of personal data provided by the airline - does not.
It seems that I'm not alone. Congress is currently reacting badly to requests for more money for US-VISIT, saying that there are huge holes and a dismal lack of strategy. It doesn't know where it's going, but it's not going there very well - so why should Uncle Sam buy it new toys? (It wants ten-finger fingerprinting, instead of just the two digits it scans at the moment).
The major problem is that although it logs everyone coming into the US, it's not very good at spotting them leaving. There are some experimental kiosks around with automated fingerprint scanners and passport readers - San Francisco has some - but they're easy to miss, and the consequences if you pass them by aren't clear. It's a bit like losing the counterfoil to your visa waiver form: in principle, you hand this back to the check-in staff when you fly home, but it's easy for you or them to lose it. (One friend who did lose theirs was told by the check-in staff to on no account tell anyone. This proved the right advice, as there were no further problems: a friend who also lost thers and did the Right Thing by telling the US immigration people has been put through the mill, having to get solicitors to write notarised latters, presenting herself with bank statements at the US Embassy, and generally being treated as a cheating, lying scumbag intent on... well, she's not sure and neither am I).
And another close personal friend could still be in the US, had they so chosen. They logged out of the country with the full US-VISIT fingerprint and webcam ceremony, and were quietly sitting in the departure lounge for the plane home, when the airline staff said "We're overbooked, does anyone want to stay over for another night?". As it happened, my close personal friend could think of nothing finer, and he did indeed win. Being a chap interested in procedural aspects of security, he was looking forward to finding out how they unwound the fact that he had now officially left the country: would he have to be logged back in with the full security and immigration checks, or would he just have to get his exit rescinded?
In the event, he and his fellow bouncees were rounded up by the airline staff and led off to a small door next to the departure lounge. They stepped through - to find themselves in the main hall, their bags deposited in a pile next to the entrance and the bus waiting outside. That was it. Had he legged it into the Montana badlands, he could be there still.
Oddly, he had no interest in staying in the US - an attitude that is met with rank disbelief by anyone further west than Greenland.