Been using it since I was in high school (20 years ago! Yikes, I feel old now!!) Huge fan. On the windshield of a new vehicle, it usually takes two coats a couple of days apart to get it on there thoroughly. Not sure why, but it's always been my experience that the first coat doesn't take well.
Since I started using the Rain-X washer fluids, it lasts even longer and seldom needs to be reapplied but maybe every second or third year for the windshield. (Usually twice a year if I use the cheap washer fluid) The side-glass and rear window will go several years as well.