Generally if the carry-on rules are enforced there aren't any problems. This means oversize bags are identified before they get near the aircraft and checked. Simple.

Now, I'm painting myself into a corner here as I have one of those specially contoured Tumi carry on bags. It fits the vast majority of overheads absolutely perfectly, wheels out, with the top of the case shaped to fit the back of the locker. That said - it IS too big than the sizing cages that you sometimes see at the gate.