At the Norway/Sweden border, although there are unmanned crossings, you're not allowed to cross these in a HGV- they must go to a manned crossing and fill in paperwork. There is an active border force to try and catch smugglers, and they can check people's passports if they want to (even in the Schengen zone). None of this would be acceptable in NI.
I think it's similar in Switzerland, in that checks can and do take place- just not everywhere or all the time. There are flying squads of Swiss border guards that can stop any car anywhere to check for smuggled goods and can check the occupants' ID cards. There is border infrastructure in place on the main routes. Again, none of this would be acceptable on the island of Ireland.
Despite what people have suggested, I can't see how a fully automated system would work without some kind of check to back it up? Otherwise, there would be smuggling of both goods and people across the border, surely? If you saw a car cross on ANPR that wasn't supposed to be crossing, presumably someone would do something about it? Otherwise, what's the point?
I really do think the only solution (other than staying in the EU ;) ) is to have different rules for NI, and a border between NI and rUK- so ID checks and customs checks on ferries and planes. It might be unpalatable to the DUP, but it's the only solution to save the GFA. And if the UK breaks the GFA, not only will we restart the troubles, why would any country in the world sign a deal with us ever again? No-one will trust us or want to sign trade deals with us.
Someone really should have considered this issue before opening up the issue to a referendum. It would be such tragic irony for David Cameron to ultimately cause the break up of the UK.