I remember bumping my new Lexus into a car in front at a traffic light on Christmas eve a couple of years back...I was coming to a stop, but looked down for a second to pick up a credit card that I'd dropped next to the car seat...and hey! I was stopping...only a little bump that caused the hood to telescope out and cost me a pretty penny, made my insurance go up! (noone was hurt)
Therefore, I do think there's merit to California's new law - hands-free calling is better than no-hands-on-wheel, especially on the freeways!
Now, if only Apple created a pair of earphones that work with my iPhone and actually stay in my ears!!