They're a mixed blessing, for sure.

There are a couple of demonstrable improvements for driving, but they don't
appeal to everyone and for some, the peculiarities like windshield spots
outweigh the benefits.

On the plus side, polarized glasses dramatically reduce windshield
reflections when you store a map or route sheet or clipboard on the dash.
Most people won't leave white paper on the dashboard, because this
particular angle creates disabling reflections in full sun, which drop by
about 80% with "correctly" polarized lenses. Of course, it only works
straight-ahead. Polarized lenses actually _increase_ glare over a small area
in front of the passenger. His clipboard will bother you, your clipboard
won't.

The fact you're seeing "spots" in side and rear windshields confirms that
your lenses are effectively polarized. The "spots" are interspersed with
"holes" you can see through, which all turn to bright nothingness when you
take off the glasses.

Occasionally, sunglasses get made with the orientations exactly 90 degrees
_off_. In that case, all drugstore sunglasses look totally black and the
dashboard reflections are intense, rather than subdued.

-MT

Right. And from my experience, polarized sunglasses don't make any
noticeable improvements in driving conditions, and even have some
negative effect. Maybe they're better for beach/ocean/lake conditions,
but not on land.

In order to provide optimum polarization, the glare must be coming from a
specific angle. A polarized lens "effectively" has thousands of small slits
that blocks out direct reflections of the sun (sort of like Venetian blinds)
but still let light in. But the slits must be at the correct angle, just
like blinds can be adjusted to block out the direct sun but still let most
of the light in.

A polarized filter used on cameras can be rotated so the slits are aligned
correctly for the glare in a particular scene. In eye wear, the manufacturer
just assumes the glare is coming from a particular angle (since obviously
the eye lens cannot be rotated), and if your glare comes from a different
angle than designed for, it will not be blocked. In other words, a polarized
lens cannot block glare from all angles at the same time.

I bought a quality pair of polarized sunglasses (Hobie, $60 sale/$160
retail) for driving purposes, especially to help in daylight rainy
conditions. I read about the theory of polarized light, and thought it
would be a great improvement over regular sunglasses. However, I've a
been quite disappointed in their performance.

Whenever I came across a situation that I thought should make a
difference (like sun reflecting off a wet road, or drizzling
conditions), I compared the polarized sunglasses vs a non-polarized $5
sunglasses. I honestly couldn't notice any difference in glare
reduction.

On the other hand, polarized lenses had some negative effects. LCD
displays (radio, odometer) have a disconcerting shimmer (because my L
and R eyes see different brightness due to their different angles).
When I looking at other cars' windshields, I see a disconcerting
effect of a grid of spots (possibly due to safety glass?) And I can
barely see a rainbow! =)

What are other people's experiences with polarized sunglasses? They'd
probably be really great if you're at the beach or on the water, but
for land and driving use, I think I'll get non-polarized next time.

http://www.hobiepolarized.com/eyewear.aspx