Weedwhacker said:Normally when I wash the windows there isn't any water or pail involved in the process -- I spray with Windex, use a paper towel or 2 for the initial cleaning, then use a clean, dry microfiber cloth to finish it off. The windows then look great until the sun hits them... 
That just made me think -- maybe I should try some other type of paper towels? We always buy Bounty; I wonder if they have some kind of "additive" in the paper that could be causing the streaking?
Toss the microfiber piece in the garbage, no wait, burn the sucker.
Microfiber is plastic, plastic does not work like natural fibers.
Cotton absorbs grease, microfiber smears grease.
I only use natural fiber cloth.
The fact there is stuff to smear on your windows means your cleaner is not removing it.
Alcohol cuts grease, try wetting a cloth, I mean dripping wet, with alcohol and use just that to clean, then use a dry paper towel to wipe it off.
This is how I finally got the scum off of the inside of a several car windshields.
There are often, even on new cars, oil vapors under the hood and your ventilation system gets some of it air from that area putting oil on the inside of the windshield.
If you air-conditioner has even a slight leak there is oil in that system that will also end up on our windshield.
