I don't like the idea of leaving the gun in the car. It's in it's holster when I'm driving, and when I get out it stays there. If a cop inquires as to weapons, then I'll tell him about the gun and hand him my license, but until then I think it's best not to introduce it into the situation unnecessarily. My state has no "duty to inform" requirement unless the officer asks.
Another thing to consider is that leaving the gun in the car may be considered irresponsible or worse, especially if there are other people in the vehicle and none of them are licensed to conceal.
This is coming from a very easygoing person in a low-pressure area who has never had a collision, so take it for what it's worth.