Correct me if I'm wrong, but at least when entering the US by car, you're already on american soil when talking to the border patrol. On a ski trip to Jay Peak, two stupid heas brought marijuana with them. But was searched, border patrol found it. All three were then detained for investigation.

I'm from Canada. I've been in the US dozens of times (last time being two weeks ago) and my fingerprints were never taken from a border patrol. I had some bad stories at the borders though.

DUI (driving with more than 0.08) is only for motor driving (car, boat, snowmobile, tractor, plane).
But you still can get a ticket for riding a horse while drunk, though the consequences are a lot less important. A 100$ ticket.
http://lejournaldequebec.canoe.ca/journaldequebec/actualites/quebec/archives/2009/01/20090123-120605.html/ Two months ago in Trois-RiviÃres.

In Quebec, it also applies on private land. Same ticket if you're caught having a beer on a lawn tractor in your yard than while driving a car on the road.

Why do you think I precised where I live and that these numbers are for our farm? Beef farms in Abitibi-Témiscaminque (~48 degrees north, still in Quebec, rocky peaty soil) raise their beef with grass. But they still complete part of their diet with corn. I do know that this is not the case worldwide.