Is it okay to cook with olive oil?

Depending on the amount of heat, olive oil does have a smoke point (320 degrees Fahrenheit or less) and at that point, the molecular structure of the fat changes and you no longer receive the benefit.

If you are using it for flavor or to keep things from sticking to the pan, etc, it is fine. If you are trying to up your fat intake, it is best to add it after the food is removed from the heat.