I have noticed lately with all the slop many vehicles like my mini van have a back windshield wiper. Besides mini vans, this includes SUVs and autos. While the rear wipers are handy, here is some words of caution.

Scratched Glass - If the back window has gotten nasty, you might want to get out and clean it with some glass cleaner. Do that instead of turning on the windshield wiper and washer to prevent scratches. I find many times the wiper blade may make a couple of sweeps before the washer kicks in. During that time the dry wiper is performing like sand paper on the glass. The result I've seen is severely scratched glass.

Check Your Rear Wiper Blade - While the front wipers are easily seen and checked, the rear blade many times isn't. Studies have found that the front blades are replaced twice as often as the rear. Just like in front a bad rear wiper will quickly scratch and destroy a rear glass.

Finally I found a blog with art work on the back glass. This is cool what this guy can do with a dirty car window. Link: Dusty Windshield Art