Here's a link to the FAQ page on tint laws in this area:
http://dcmetrominis.org/forum/topic/4628-what-are-the-state-laws-regarding-car-window-tint/
Cricket was originally a DC resident, but I wanted tint, so I had it done VA legal (50% all around - I didn't want it darker in the back). I never had an issue with the DC police, but I didn't do anything crazy, either. Now that she's an MD resident, I'd love to get her retinted to 35% all around, but it's expensive (and time consuming) to remove the old tint.