Obviously that's not a UA only problem. If carry-on rules were uniformly enforced, there would typically be plenty of overhead space, and I for one would not rush to get on the plane. If there were plenty of overhead space, I would be glad to be the LAST one on the plane! Unfortunately, the employees of many businesses don't realize the value of being consistant! If people were told every time that they couldn't bring their steamer trunk on, then they would stop trying to bring it on. But if they are only stopped 50% of the time, they will keep bringing it on, and be pissy with the employee who rightly told them no! Sigh....someday!