Originally posted by: Dhawk
Chances are none of the stuff mentioned above will return your windshield to pristine condition. If your car has it's original windshield, it is most likely has been sand blasted from years of exposure to the fine sand and dirt hitting the windshield. Think about this, when following other vehicles at highway speed, their tires kick up dirt and sand on the road. Add to the fact that it is being kicked up from tires going 50 to 70? Mph and then hitting your car going the same speed, it will eventually create thousands of little tiny pits in your windshield. Those little tiny pits will affect the clarity of the glass by themselves, but they also create a more porous windshield that will hold road dirt and film easier.
Also, if your wipers are not changed regularly (it's recommended every 6 months), they too will damage the clarity of your windshield. Oh, and if you turn your wipers on when the glass is dirty, same thing even faster.
I have seen windshields sandblaster like I mentioned above in less than six months use.
The only remedy is to replace the glass if that is the case.