I've used Rain-X for years and have never had a problem with it, but I know many people who have tried it and hated it as well. I find that it's more in the application than the product. First of all, a clean windshield is a slick windshield to begin with (you don't apply your lsp before fully prepping your paint do you?) and secondly, most people don't understand the purposes of rain-x.
I only use the original rain-x in the bottle, not the spray, and I always take my time applying and letting haze, then buffing off...and I really mean BUFFING off! I find most people that complain about wiper streaking and haze are the people who don't put the work into removing the product (obviously the distilled water helps make it easier if you don't want to work as hard, but I do it the hard way). Then I apply a second coat, let haze, and buff off again, making sure not to miss any spots (I even use distilled water here occasionally). Using this method, I've never had a single problem with my wipers streaking, window hazing, or other problems on my truck nor any other vehicle I've applied it to, including customers who have previously had problems with rain-x.
Rain-x is designed to let water bead and run immediately off the windshield, which allows you to drive without even using your wipers (Except in extreme conditions, and even then I barely use mine) because it is actually clearer than having the wipers going back and forth. Given proper application and upkeep (just like paint) I find that I almost never use my wiper blades, and I live in Florida. The only time I need them is when there's barely a sprinkle coming down and I'm not moving fast enough (20-25mph +) to run the water off. I still maintain my wipers and replace them regularly because in the event that I forget to reapply rain-x and it wears off and I realize it while in a storm, I like to know my wipers are going to work then!
In the end, as with every other automotive product, there are going to be extreme differences of opinion, so to each their own.
