I've been prowling these boards trying to determine whether trucking is a good career choice for me when I came upon this thread regarding using Rain-X on your truck windshields.
I have used Rain-X on my various personal vehicles and have always been disappointed by the smearing and the constantly having to reapply. When I had my truck accessories business I sold a product called Aquapel by PPG. It is not silicone based like Rain-X, lasts about 6 to 10 months per application and doesn't smear. You cannot tell it's there except when it's raining. I've had huge rain drops burst into millions of tiny droplets. Applicators generally charge $15 to $20 per application. Automotive paint supply stores sell it in single application vials. Really cool stuff. The following link will take you to the Aquapel page at the PPG site.
http://www.ppg.com/gls_aquapel/default.htm
Just my 2 cents worth.