the only window you're allowed to have tinted is your rear most window. (this pertains to smaller cars, sedans, wagons, etc)
i had 20% tint on all my windows on my wagon, i've been pulled over and ticketed about 7 times in the past three years. they probably would've never noticed me if it wasn't for my loud exhaust, but i've only gotten 1 exhaust ticket. weird.
i removed my back window tint because it got scratched up pretty bad and i haven't gotten pulled over since, probably because the cops can see through the back window when they're behind me and that makes them think i don't have any other windows tinted. lol.