Canada?
I did a mileage run last year with a turn (2.5 hours) in YVR. Had to speak to 3 immigration and 1 customs official which burned nearly 2 of those hours. When I explained to all 3 Canadian immigration officials my reason for the trip they looked at me as if it was the first time they had ever heard of this. I guess it all depends on where you go and who you speak to but I did find it hard to believe that 3 immigration officers working at an airport would be unfamiliar with mileage runs.