Could be very painful & I take no joy in that.
At one time I flew freight daily between the U.S.A and Canada. Two of my worst aviation experiences involve U.S. Customs occurred during that period of my career.
Your experience will vary between custom inspectors. If you happen to draw a lousy inspector on one of their bad days you may be in for a very rough ride. I got hit with a $10,000 fine once because the "young buck" did not like being kept waiting on a Friday afternoon and was in a nasty mood when I showed up. There is no point in rehashing the details; the end result was the fine was waived and no action against me.
My neighbor retired from U.S. Customs service. He was a great man (deceased now) served his country well and did a commendable job. I am sure there are thousands just like him employed by U.S. Customs. As inspectors they have a lot of authority and power; not all of them wield them wisely or equitably. To be fair sometimes the Custom inspectors have to deal with idiots and other times with the criminal element (there is a reason U.S. Custom inspectors are armed). I know it goes both ways.
Remember: U.S. Customs can be a very hostile adversary. I do not like dealing with them and that is coming from a U.S. Citizen with nothing to hide.
ADCUS on a flight plan, email to a FBO or some other method may not result in proper notification. Proper notification is your responsibility as PIC of an international flight. If something goes wrong U.S. Customs can in fact "hammer" you. Whether or not the heavy hand of U.S. Customs comes down on you depends on your attitude, disposition, level of humility in dealing with the inspector on duty, the inspector's disposition that given day and whatever else is going on with the inspectors job and career including the pressure they themselves may be feeling.
During the preparation and preflight phase of your flight you were in control and in position to dictate most of the eventual outcome of your clearing customs in the United States. Now that the border crossing is in the past tense; you no longer have as much influence over the end result. I hope it goes well for you.
Last edited by Northbeach; 15th October 2011 at 13:07.