a couple of thoughts:

i quit using rain-x on the front windshield because it worked too well ...
i noticed that i was driving faster than i really should have, because my
visual information was messed up: the water wasn't staying on the windshield
so i didn't "think" it was raining as hard as it really was.

however, for those of you who do use it, also put it on your outside
rearview mirrors and rear window and drivers window: it keeps the morning
dew-fog from forming, so you don't have to wipe them off to start driving.
don't know if it will work on snow. ;)

windshield polish: we polished my nephew's windshield with some extremely
fine paint/body polish (rubbing compound) and it made a tremendous difference
... it got all kinds of stuff off the glass, made it really really really
clean. it also made the water bead up, like rain-x. eventually, it wears off
though ... and i thought surely it would smear from the wipers, but it didn't.

joel