some interesting info on polarization.
normal sunlight has no direction (incoherent). once it reflects off of something it becomes polarized, hence why polarized sunglasses works so well at cutting down road glare, (or light off snow, or lets you see through the surface of water more easily.)
another interesting point of note (which i have to worry about in my job as a mechanical engineer) is that when you mold plastic any molded in stresses will come out as polarized. this happens especially when the molten plastic needs to move around some features or when it goes from thin to thick or vice versa. you can't normally tell the difference, but if you wear polarized sunglasses then they show up as these rainbows (or the crazy check pattern in pre-stressed/tempered auto glass.)
now to put the two together, cheap sunglasses aren't very well consistently polarized (look at one pair with another pair). more expensive lenses will have less "stress" markers and will behave more consistently at cutting down glare.
one annoying attribute that some have mentioned is that when dealing with two polarized lenses (or glasses and lcds) if they are 90 degrees off from one another then the view blacks out. like when i can't see my gear indicator with my glasses on, but if i put my visor down, it messes the alignment up enough to make it visible again.
the more you know. .
