I run right around 35psi up front, but lately have been putting 45 in the rears. Here's my thinking - take it as you wish: Street radials will "crown" if you put too much air in them, allowing only the center of the tire to contact the road. Underinflate them and they will actually go a bit concave at the center, essentially just running on the outer edges. If you've ever seen those tread wear indicator photos where they show how unevenly a tire wears if under- or overinflated you know what I mean. So basically, to get the largest contact patch (and presumably best traction) out of street tires I recommend the, um, well, recommended pressure.
My rationale for higher pressures in the rears is simply for lower rolling resistance - heck, you're just towing those tires behind you, it's not like they do anything other than keep the back bumper from rubbing on the street!
