I've known people to get tickets for their tint in Nashville, but I've known several who haven't. I have fading mirror (now illegal) and never been questioned in 5 years. It's hit or miss, just don't piss off the cops and you'll be fine with 20%.
As far as tails, I think the official law is that blacked out headlights AND/OR taillights at night is illegal, but it's never enforced. It was made into law when blackout headlight covers became popular in the mid-90's... don't know of anybody who enforces it though.