I run my 2008 HHR LS at 37psi cold because that's what works best for us. Appropriate tire pressure depends a lot on how the vehicle is used. Many tire shops think the rating on the tire is what it should be inflated to.
My GMC truck calls for 80 in the rears and 55 in the fronts. I run it 75 in the rear and 65 in the front (most of the time).

 

Well, I guess this is a good time to remind us about the little problem that Ford and Firestone had and the reason that we have to pay for ESC and TPMS on our cars. People die because they can't be bothered with tire air pressure. monitoring.

Over inflation leads to instability, there is less rubber on the road and the center of gravity is higher. The reasons that some people cite for under inflating.

Under inflation leads to over heating and sidewall failure due to the flexing of the sidewall.

The "max inflation" on the sidewall is there because if you go above that there is a chance that the bead could fail, leaving you flipping.

Not even getting into excessive wear from either.

If the placard on the car has a higher PSI than the max PSI on the tire it is because you have the wrong tires on the car.