Another thing to use (besides cleaning the blades) is to use a fine grit sandpaper and fold it in half so the sand paper is facing in, and go over the rubber blades 1-2 times to renew them. Under a microscope the blade (brand new) is smooth and covers the whole wiping area. After a few months of wiping water, grit, sand, dust, and road stuff the blades become pitted.
Only bad thing about Rain-X is that it will eat away at your windshield wiper blades quicker. So in the long run you might be paying more for blades. The chemicals in Rain-X dry out your wiper blades quicker.
By the way, WD-40 and Rain-X have the same basic properties. Just for your info