Tire pressure is a subjective thing, and matters more if you have high performance tires. When I had summer tires, varying the tire pressure by 2-3 psi would greatly affect handling, response and ride. I'd put my rears a bit higher to neutralize understeer a bit. I keep my winter tires at around 38 psi because the higher pressure provides less rolling resistance and thus increases gas mileage slightly. The ride is also a bit firmer but I don't care.

For people like you, do what it says in the owners manual and your door jamb so you don't screw anything up. This probably means 32 or 33 psi.

Oh yeah, and tire pressure changes surprisingly dramatically with temperature changes.

And your problem is probably your alignment or unbalanced wheels.