In NJ, no tint is allowed on the front windows or windshield by law. I had a Cherokee with 5% on every window, and an 8 inch strip along the top of the windshield. Couldn't see a damn thing in my mirrors at night. I eventually mounted Fog Lights inside facing out the rear window with custom little rubber housings I made to keep the reflection out. Was great for blinding tailgaters. Cops would say something about my tint once in a while, but luckily I was able to talk my way out of being handed a razor blade to remove it. I don't know about other states, but in NJ - some cops will give you the option of either removing your tint, or having your car towed.
That being said, my Protege has 35% tint. It's not so noticable as some peoples tint. Also, my cars color helps it blend in with traffic. I still put down both windows in the front whenever I get pulled over, or when I think a cop may be looking.
I would have gotten 50% tint, but my friend was hooking me up at his shop - and he was almost out of 50%. 50% looks very classy. It's a light tint, but really gives the car a nice look.