just tonight we upgraded our ceiling fan to a ceiling fan/light so can finally have good room-fill in our living-room. However just now (like 2 hours after install) I realized I may have forgotten to install the suport hook so it is only being held up with the 3 screws and the hinge hook on the outside. How critical is it that I pull the screws out and attach that hook if I did in fact forget it?
Quite critical -- an improperly installed fan is a trap waiting to fall on an unsuspecting occupant's head! I'd fix it straight away (and double check to make sure you didn't damage the parts that are currently holding the ceiling fan up, too)!