Power Button Question

On the Macbook Pro using Leopard;

I'll be letting my wife use the computer for some work and I'm a bit 
nervous about the power button. If for some reason she forgets to shut 
down normally and pushes the power button with the system up and 
running, what exactly happens at that point? I've never done it on a 
Mac. Does it execute a hard shutdown or throw you an option window?
Thanks
-- 
Dudley Henriques