Three ounces? Does it have a lead mount? <img src="/forums/images/graemlins/tongue.gif" alt="" />

I find pola filters basically a requirement, especially with wide angle lenses. Your water demonstration is a good one; they also cut airborne haze, making for bluer skies and highlighting clouds. They can also enhance colors of certain subjects, such as flowers, by cutting scattered surface reflections.

A caution: Any camera that uses beam splitting for metering or autofocus (most modern digital cameras) needs a "circular" polarizer to work correctly. The less expensive linear polarizer will interfere with these functions in certain situations. Circular polarizers can get expensive, especially when you get into the multi-coated variety, so the suggestion about shopping around is an excellent one. I've gotten a couple used and significant discounts.