I only have 15% and i think ~30% is legal here. At first I thought holy crap, this is too dark at night, but I got used to it. I've even thought about going back and getting another layer. i'd go around 10% probably, if i had it to do again.
I have 35 on my sides and 20 in the rear. 35 all arround is legal for VA. If I ever had it redone, I'd probably get 10 all the way arround. I gave my stepdad $175 one day and told him to get the guy at work (at his body shop) to do it. And I guess he asked the guy to do legal. Oh well.