That's funny, because my S came with the entire rear window tinted...and I want the cut out near the
 

third brake light. Sure, it doesn't look pretty, but I actually believe having a clearly visible third brake light is a good thing, especially with tint, because people can not see through your car to the traffic in front of you.

luv my polarized sunglass. what a difference. it was really weird for a few days being able to see
 

into peeps cars with tint, since the glare would block your view. good tip.

That splotchy appearance on factory tinted windows is normal.
 

You'll see that on almost all high line cars (MB, BMW, Audi, Porsche) when you're wearing polarized lenses. Aftermarket tint makes it less apparent, but the color variations are still there.

One whole piece on the back glass.

Not true. With any polarized sunglasses, I could see dots/color changes in OEM tint on any car...
 

Mercedes, BMW, Audi, Jeep, doesn't matter. The polarized lenses and the tint make the difference, not the quality of tint job. I was sunglass shopping and some lenses did it and some didn't. Some did it on certain cars, others did it on others, so I decided to get non-polarized and I love them!

Re: as dark as you can go, i dont know the %