One of my friends (UA Silver status) received an op-up from Y-J on UA53 ZRH-IAD today... Y was not oversold... in fact there were still 15+ seats open. Not sure how that happened considering he was on a K fare. I have only had 1 op-up on an int'l, and that was when they were in a desperate situation to bump people from the flight, and they filled out remaining J/F inventory by upgrading people from Y/J to minimize the damage.