I used to have a limo black on the rear window and then all the sides done in a dark tint. Looking back, it may have been a bit over the top. I had the rear window done professionally (curved glass is a pig for bubbles, you need professional tint film which is a little bit more forgiving and stretches a little). I did the side ones myself as they were flat. Just have to clean the glass within and inch of it's life. I like to use a razor blade held flat to the glass to scrape all the bits off with a good quality glass cleaner. Turned out nice.
I'd just do a light tint all round now, to avoid looking like a drug dealer.
It did mean the inside of the car was very, erm how shall we say? Private at night, when I used to be driving girls around. Did you know the little handle straps on the b-pillars make great stirrups for girls feet to go through? God bless the designers at VW for coming up with that one.
!!!WARNING!!! non cal look picture content. Do not click if easily offended! I was in my drugs phase at the time and heavily in to hotwheels!
http://i9.photobucket.com/albums/a51/UnmuffledRyan/Bug/001-3.jpg