My son leaves this Friday - I'll post the result but the crux of the issue is that you need to hand over your visa when you leave the USA for Canada and that way you have left the US. The bit that is causing some people confusion is that if they leave say LAX for Canada and they don't surrender...
This is the response I got from the horse's mouth:
Discussion Thread
Response (Mark)
09/25/2009 11:47 AM
There should not be any issues for your son to come back through the US. When he first arrives in LAX he will be a given a green I-94W...
