I popped in to my local Pentagon office yesterday. I was initially after light-smoke all around as I wanted it a bit darker, but not to the point of drawing unecessary attention. However, as I have a very light interior they've recommended I go for "smoke" otherwise the change would be minimal.
The cost of covering all of the CLK ('cept the windscreen of course) was £260, which I think is a great price. They're the best guys around, and when I asked in they could be removed, say when I sold the car or if I was unlucky enough to be told to remove them by the police they said that not only would they do this for free, but they're replace it with a light-smoke option if I so desired.
My wife's car (Lexus RX300) came with limo black windows in the rear from the factory and I think it looks excellent. It all depends on the kind of car IMO. 4X4s can pull it off, but coupes with smaller windows could look silly. Whilst I was at Pentagon they showed me a few models which had light-smoke at the front and smoke at the back, and they looked great - they sort of blended together and there wasn't such a stark contrast.
I'm booked in for my fitting next Wednesday, I can let you know how I get on if you like?