[spacemanspiff01]

They do, or at least when I last flew they were charging people who had carryon bags that would not go beneath the seat.

(I had a backpack that was slightly oversized, but they did not seem to care that much.)

[tomschwiha]

I guess it depends on how full a flight is. A empty one they don't really care - a full one they care more. But also if its a cheap or "premium" airline.