I run my 31s at around 28psi for street use (much lower and it "chops" the shoulders, much more and the ride is harsh. Remember, the larger the tire, the less pressure you need (it's the VOLUME of air that holds the jeep up). Play around to see what works for you.
For serious off road use, lower your pressures WAY down (like 15 at the most, depending on the terrain). Makes sure you have a way to air them back up for the ride home