I have a friend here in Dunedin, NZ (not a window cleaner), who used RainX on all of his house windows over a year ago. Ran into him a week or so back. He is absolutely rapt. Has hosed (read, not bladed or brushed) his windows ONCE and they still are up to his wife's quite stringent standards. bit annoyed actually as I was hoping to get a call... Not saying this is THE answer, but, it certainly appears to be AN answer, for some glass.